BITSAT Most Expected Physics Questions | BITSAT 2023 | Shreyas

hello Mario Warriors can you guys see me and hear me loud and clear do let me know in the chat box I hope I'm horrible visible this is your captain and I'm going to navigate you through this Rough Waters that you are in the hurricane that you are in after J Mains first and the second attempt and that is bedtime the good thing for us is website has two attempts so we'll try and crack it in the first attempt itself and we'll have our full our focus on it but remember don't feel disheartened at any point even if you are not getting problems or if you feel that no I did not do much in J I've been uh you know regretting so many things I should not have done this I should not have done that forget all those things just focus on the bedside examination because if you get through this examination trust me you will be in one of the India's finest College comparable to iits and nits okay so let's begin with the class and today's class is basically the most expected questions and in a form of a mock test they all know bitside has 30 questions in physics so I'll be solving around 25 questions I guess in physics and the five questions I will be giving you as homework where will you get the homework just go to the telegram Channel download the PDF you will get those homework questions okay hello zodiac hello all the students who are joining in live do not forget to mark your attendance by Smashing that like button and also hitting the Subscribe Button as well okay so it's time that we begin our class ready my dear students and ready for the first question okay so looks like everybody should be ready by now and you have smash that like button thank you so much and subscribe to the channel so that you do not miss any other updates okay so here comes the first question on your screen now if the coefficient of cubicle expansion is x times the coefficient of superficial expansion then what is the value of x see coefficient of basically we are talking about cubicle expansion that just means basically gamma correct then what is the meaning of superficial expansion my dear students superficial means aerial area expansion so that is basically beta now we all know gamma is basically three times of alpha three dimensions so three times of Alpha and beta is basically two times of alpha everybody knows this yes or no my dear students perfect till this point very good very good I hope I'm audible guys just let me know okay everybody know yes I think I'm audible okay cool now now if you just divide both of these numbers gamma by Beta alpha alpha cancels it will become 3 by 2 that means it will become 1.5 times so what is that X this is 1.5 times so if gamma is x times beta so that is basically 1.5 times of it hence the correct answer for this question is option C 1.5 okay usually you will see bits are questions are pretty much straightforward simple very few even average above average questions come and time is of essence over here you should be solving uh one question in 40 seconds to Max 50 seconds not more than that okay next on an average I'm saying next a body is weighing 700 Newton on Earth what will be the weight on a planet having 1 7 to the Earth's mass and the radius is half of that of the Earth how is weight related to acceleration due to gravity think weight is mass into acceleration due to gravity so gravity will change and what is the formula for acceleration due to gravity it is G which is your Universal gravitational constant mass of the earth divided by the radius square isn't that so that is the formula now see carefully what has happened in that planet if I say G Prime mass is basically 1 7 so M by 7 radius is half so R by 2 whole Square so this will become g m by 7 R square 2 square is 4 4 will go on the top 4 will go on the top now we all know GM by R square is G so it will basically become four by seven look at these numbers guys this number 4 and 7 is constant GM by R square g m bar R square is basically G so why not just write it as G so the acceleration due to gravity has become 4 7 times acceleration due to gravity has become how many times my dear students 4 7 times I hope this is very very clear so what will happen to that weight it will also become 4 7 times of that old weight so basically it will become 4 by 7 of 700 that means it will be 4 into 100 which is 400 Newton so 400 Newton should be the answer that is option D of course yes definitely the correct answer is option D very good guys very good keep it up keep it moving moving on to the next question on your screen remember these questions are direct questions which will come in bits at exactly bits at level so you should be trying and solving this within one minute okay one minute is like the worst scenario okay very difficult questions might go over one minute but every question try to finish it definitely within 40 seconds Max to Max and rare guess okay in one minute okay uh a man fires a bullet standing between two clips first Echo after three seconds second Echo after five seconds what is the distance between the cliff the speed of the sound is given so here is what I will think Imagine One Cliff is here another Cliff is here our pandu is let's say standing over here okay this is our pandu so the sound will travel like this turn and come back the sound will travel like this that's what an echo is right it will reflect and come back the one which is closer it comes back in three seconds the one inches farther comes back in five seconds right that is what is happening now assume that this side distance is D2 assume this side distance is let's say D1 we have to find what is the total distance think about it D1 is this distance okay I can write in one particular way think carefully guys the sound is going and coming back so it is traveling the distance twice so the total distance traveled by the sound is 2d1 because D1 while going D1 while coming back so 2 d 1 is the distance that distance is speed into time speed into time what is that speed it is basically 330 yes it is 330 and into that time what is that time it is 5 Seconds same way D2 will be traveled two times while going and coming back the total distance will be that speed into that time which is 330 into basically three now the total distance ready will be D1 plus D2 D1 plus D2 now can you see guys from here D1 is basically 330 into 5 by 2 and D2 from here if you take that 2 below is 330 into 3 divided by 2 just take that 2 below that's all I have done correct so D1 plus D2 will be nothing but 330 by 2 is common and 5 plus 3 is there in the brackets right 5 plus 3 is there in the back brackets so this will become 330 by 2 into basically 8 2 goes with 8 4 times 33 into 4 guys what is the answer come on that is going to be 132 put that extra 0 so that's it that is the answer that is the answer one three two zero where is it option b yes option b very good Aryan very good proud of all of you very good karthikian very good excellent idea Warrior so that is the correct answer okay moving on to the next question so whenever you see Echo questions remember the distance is always traveled tight twice if you miss that number two that's it you will get a wrong answer you will get incorrect answer okay the ratio of the displacement of the body in eight seconds to the displacement in eighth second if starting from rest with acceleration of 20 is okay let's see if you guys can solve this particular question the question says displacement in eight seconds upon displacement in eighth second what is the formula displacement in eight seconds I will use normal u t plus half a t Square so I'll use u t plus half a t square formula and for nth second the formula is U plus a by 2 into two n minus 1 that is the formula initial speed is 0 because it started from rest initial speed is zero so what will come in the numerator guys think about it 0 plus half into acceleration into time time is basically eight Square divided by 0 plus again a by 2 into 2 into 8 minus 1 okay 2 into 8 minus one half half a a gets canceled a half a and half gets canceled what is the remaining my dear students is just 8 square in divided by 2 into 8 minus 1 8 square is 64. a 2 is a 16 16 minus 1 is 15. so 64 by 15 60 4 by I think that one is missing somewhere uh I think that one is missing somewhere okay so I think the answer marked is wrong over here yep so the correct answer should have been I'll just put it up over here guys okay answer Mark over here is slightly wrong so it should have been basically 64 by 15. this is the correct answer okay everybody with me very good guys awesomeness awesomeness shall we move ahead to the next question shall we move on to the next question very good question keep answering guys I also feel happy that you guys are solving along with me and if you face any difficulty you are always free to look at the solutions on how I am doing this okay moving on to the next question if a planet is made of a satellite whose mass and radius were both half of that of Earth then the Escape speed for that satellite on the surface will be how much imagine there is a planet whose mass is also half radius is also half as that over so for the satellite to escape that planet what do you think the Escape speed on its surface will be hello nigma guys make sure your smash the like button guys show support for the channel and to me as well your captain your yes your guide your Navigator make sure you do that okay so come on my dear students what do you think is the correct answer for that option A is it okay let's try to think what is the escape speed formula what is the escape speed formula it is basically root of 2 times of GM divided by R now see what is happening guys the mass is becoming half radius is also becoming half one is in the numerator one is in the denominator half and half cancels so that means the Escape speed will remain the same it will be same so on Earth what is it it is 11.2 kilometers per second this is meter this is meter meter will not be correct so many students did not look at the units it is kilometers kilometers per second so guys if you made that blunder you will definitely get Negative marks you cannot do that okay so that's why the options are a little confusing and deliberately it has been put in that way because many students will fall for that particular trap okay moving on to the next question coming up on your screen the speed of a ball of radius 2 centimeter in a viscous fluid is 20. if that same liquid is used but the radius of the ball is one then what do you think will be the new speed I think viscosity speed that means it is basically terminal velocity yes lingage there will be an Avenger batch but not now it will uh come on the platform later on first we'll have a YouTube batch as soon as the match teacher joins very soon okay very soon we are going to launch the YouTube batch for j2024 okay definitely and then slowly after a few weeks definitely we will also launch the 2024 platform match on an academy platform don't worry okay now remember the terminal speed formula my dear students is 2 by 9 2 by 9 G R square Sigma minus rho divided by ETA this is the formula gets this is the formula for the terminal speed so can you not see that the terminal speed is proportional to the square of the radius so therefore V2 by V1 will be R2 by R1 whole Square final speed I don't know initial speed is 20 final radius 1 initial Radius 2 so 1 by 2 whole Square so from this I will get V2 divided by 20 guys just create a division yes V2 divided by 20 is basically 1 by 4 therefore V2 is 20 by 4 which is basically 5 centimeters per second I think that should be the answer yes option A many of you are saying option a very good yes that's the answer now this formula is very important you will get direct questions on this sometimes it could be on viscosity then it will be inversely proportional if it is on density it is directly proportional if it is on gravity it is again directly proportional to it moving on to the next question there is a source and an observer and what are they doing they both are moving away from each other okay let's think about it imagine that you have a source which is moving away so it is generating sound and the Observer or detector is going this way okay then the apparent frequency formula is given by original frequency you will have the speed of sound speed of sound so speed of the Observer remember will come on the top speed of the source will come below now because both are moving away the ratio will reduce so the numerator will reduce denominator will increase so numerator will reduce that's why negative sign denominator will increase to reduce the ratio that's why positive sign understood both are moving away don't think so both are going away no so plus plus or minus minus na many teachers or many institutes or many books also you know confuse students with the sign convention it's very simple look at the ratio whether it is increasing or decreasing numerator when it increases it increases the ratio denominator when it increases it reduces the ratio accordingly manage the signs and when you go away you reduce the frequency when you come close then you increase the frequency so my dear students over here the apparent frequency is 1950 that is very important that is the Observer finding the frequency the actual frequency means F naught so F naught has been asked and now substitute all the numbers over here so 340 340 over here or Observer speed is 10 Source speed is also 10 so basically it will be F naught 340 minus 10 is 330. this is basically 350 0 0 cancels so I will get basically F naught is equal to 1950 into 35 divided by 33 is that okay guys everyone with me great now just see if it is divisible yes it's divisible by three so this goes with 11 times if you divide this with 3 we'll get this as 6 then yeah correct and then 5 and 0. so when you do the math just check what is that they get many of you are saying option b is that so yes it is option b only guys so it is basically two zero six eight Hertz so it is basically two zero six eight Hertz only so when you do the math okay as simple as that so you will spend some time calculating that is why you should be very fast in Remembering which formula to use how to apply it whether it is plus minus you cannot waste too much time in the examination I'm telling you these questions are simple speed speed speed accuracy accuracy accuracy negative negative negative marking these things please keep in mind for bitside okay masses of the wires of copper are in the ratio one three five lengths in the ratio of 531 ratio of the resistance okay beautiful question let's try to think how to solve first of all resistance is rho L by a okay great but I want somehow masses to come into picture that means I think area of cross section will be different now I know density all right I'll just use maybe a different color density is basically mass by volume so it is mass by area into length therefore area will be mass divided by density into length so substitute that over here so let's see what do I get therefore resistance will be rho L instead of area put it as M okay because area will go on the top density comes below so mass divided by mass divided by density into l so therefore the value of resistance will become rho d L Square divided by divided by mass rho d l Square divided by mass so therefore resistance is proportional to L square and inversely proportional to the mass and inversely proportional to the Mass okay very good fine does not matter even if it was asked in cbse board exam C1 many questions will get repeated in bit set bit set has a question bank so they also uh you know after a point of time they will also run out of questions and they will have to repeat similar pattern model of questions okay so now lengths are in the ratio of look at that length is in the ratio of 531 so R1 is to R2 is to R3 will be equal to lens ratio 5 Square 3 Square 1 square mass is inversely related so masses are in the ratio one three five so one three and five will come in the denominator now what is y Square it is 25 is to 3 Square by 3 is 3 1 square by 5 is 1 by 5 multiply by 5 25 pies are 125 3 5S are fifteen one by five into five is one so 125 is to 15 is to 1 which is option D exactly are very good push that is the answer okay straightforward simple shall we move ahead to the next question guys coming up on your screen beautiful beautiful beautiful great very good awesome there is a place on Earth where horizontal component is root 3 times vertical components so many times this question would have been repeated even in normal J guys or even in CET exams so just always draw a triangle and remember the dip angle is this angle which it makes with the horizontal this is total magnetic field this is horizontal this is vertical So Tan of Delta which is the dip angle is opposite side by adjacent side the vertical component uh into three root 3 is the horizontal component so basically the horizontal component is root 3 times the vertical component as per the given information read it carefully who is who is a root three times so basically this is going to be 1 by root 3 whose 10 is 1 by root 3 obviously tan of 30 degrees hence the angle of depth should be 30 degrees it is the correct answer yes very good karthikian okay these kind of questions are very easy but many students instead of BV by BH they do BH by b instead of writing BH is root 3 times BB they write bvs root 3 times of BH so if you do that mistake you'll get to root 3 on the top if you get root 3 on the top you will think answer will be 60 degree you will Mark option A you will get Negative marks so questions are simple you need to be very careful I'm telling you now only you will realize it after the exam and you will come and tell me yes sir you are right questions were easy after coming home I was able to do almost entire paper but you know so many silly mistakes so I don't want you to say that that's why I'm telling you again and again be careful okay Hollow sphere filled with water forms a bob simple pendulum hole is there at the bottom the water slowly flows out oscillations are there measured what is the time period going to do is it going to increase remain same decrease or increase decrease whatever you think okay so let's think about a pendulum okay and I will show different scenarios for it oops okay slowly the water will come out so I feel that the center of mass will also shift guys the center of mass is definitely going to shift think about it just showing some different scenarios okay just observe this now just observe this earlier it was completely full of that liquid so it was completely filled with that particular liquid so where do you think that the center of mass will be the center of mass will be exactly over here right so this is the location where the center of mass will be now when that liquid starts to flow out you will see that the liquid will be like this there will be some gap of air on the top so Center of mass will shift away right center of muscle come down because the liquid is Flowing out so Center of mass has definitely moved downwards can you see that it has definitely moved downwards right now when more water flows out the center of mass will flow even more down but understand the mass of the water the contribution of water is even less because now the Shell's mass will start dominating and after a point when almost all that water has gone out the center of mass will again come back on the top back to the center right it will again come back to the top back to the center because only now the Shell's Mass has to be considered exactly now compare all these four diagrams and what you will use seam idea students that the center of mass shifted away from the hinge and then again came back so the length first increased so what happened to the length my dear students the length first increased and then decreased and we know time period is 2 Pi root L by G therefore the time period therefore what will happen to the time period just like how the length increase time period will increase as we decrease time period will also decrease so it increases first and then it decreases hence the correct answer should be option A it's a beautiful question on Center of mass as well as oscillations okay realize that the center of mass shifts down because the water is going down but once the water flows out the thing is left only the Shell's Mass contribution will be there so again the center of mass will come up is that okay everybody with me loved the question here comes the next one there is a body of mass uh you know a moving with a velocity B hits a body of mass C gets stuck into it what is the common velocity of the system understand what is happening guys a lot of students will make a mistake in it okay imagine there is a mass a which is moving with speed B it hits another mass of C it was initially at rest after the Collision what happens it becomes one big Mass because it gets embedded so total mass will be a plus c their final velocity will be V use conservation conservation of what momentum right conservation of momentum that's all you need to use let's see what happens guys so initial Mass a velocity B initial mass of the other guy C velocity 0 is equal to final momentum total mass a plus c into the common velocity V so it will just become a b is equal to V into a plus c rather velocity is a into B divided by a plus c so a b Upon A plus C is option b very good question Ramesh very good excellent a that is the correct answer guys proud of all of you very nice okay how many of you feel that you will be able to do these questions without silly mistakes in the actual bit set exam are you guys confident that you will do it without silly mistakes questions are easy I know you guys will be able to do it at home but will you do it in the bitside exam that is the main thing okay next question there is a boat which has a speed of five in Still Water crosses the river of one kilometer width in the shortest possible path what is the magnitude of the velocity of the river water okay now whenever you want to cross the river in the shortest possible path basically your resultant velocity should be perpendicular to the bank so imagine this is One Bank of the river this is another bank of the river okay then your net velocity will be in this direction okay okay second your net velocity will be in this direction so that you go along the shortest path because that is the shortest distance between two parallel lines which is basically that perpendicular which is drawn right that is what it is okay and that distance is basically one kilometer this speed I do not know time taken is 15 minutes which is basically 1 4 of an hour one fourth of an hour and we know time is basically Distance by speed distance is 1 speed is sorry uh speed I wanted a speed will be nothing but distance divided by time distance is 1 time is one fourth so speed will come out to be 4 kilometers per hour but this is not the speed of the river water this is not the speed of the river water the question is what is the speed of the river water how do I do that think guys that person if his total velocity should come out perpendicular actually his Strokes will be somewhere here the river will pull him towards the right side if this is the reverse speed this is the swimmer velocity U and that U has been clearly mentioned as five that has been clearly mentioned as five and we can see clearly that U square is V square plus a w Square using Pythagoras therefore W will be root of U Square minus V Square which is root of 5 Square minus 4 Square therefore W will be how much guys three kilometers per hour three kilometers per hour exactly option C very good very good option C is the correct one everybody with me understood how this question has been solved look at that triangle which is there it is also perpendicular so V square plus W square is U Square use Pythagoras very good SRI Lakshmi yes Kush very good aradhya very good Janet very good very good proud of all of you Keep It Coming guys let the answers keep on flowing moving on to the next question on your screen the moment of inertia of a regular circular disc Mass radius given in an axis parallel to the plane and passing through the center okay let's just try to visualize this disk so it's a disk okay please okay anyways right it's not obliging to become horizontal let's understand that it is horizontal or okay this is the usual axis about which I know the moment of inertia is M R square by 2 but that is not the axis about which it is asked X is in the plane and passing through the center so basically this is the axis which has been asked so I think we need to use perpendicular access theorem in fact if I draw any diameter the moment of inertia will be same whether there is this or this the moment of inertia will be same so I think we need to use perpendicular axis theorem according to that the two moment of inertia which are in the plane the axis which are in the plane their sum will be the moment of inertia perpendicular remember this green dotted line is perpendicular to this also and this also it's in that perpendicular plane right so therefore that will be equal to m r Square by 2 so basically I will get I or 2i is M R square by two two multiplies I will become m r Square by 4 so therefore I will be equal to what is the mass mass is 0.4 kg so 0.4 radius is 100 centimeter which is 1 meter divided by 4 so it is just going to be 0.1 kg meter Square that's it no it is not a many students made a mistake I think in that centimeters part guys it is not a it is option D okay it is option D many students forget that it is not the central axis instead they have given diametrical axis okay diametrical access so remember both the diameters are same guys you can leave the chapter of fluids but I'm hoping that you are going to compensate that with some other subject maybe chemistry or maths or logical reasoning and English so everybody should get full marks as do you want a session on logical reasoning and English also after math session tomorrow tomorrow I'm going to teach you maths also math smog test for bitside so next day what what say we'll do uh uh we'll do a logical reasoning in English but okay let's do the next question guys what is the angular velocity of the seconds hand of the watch okay we'll do its free I know everybody enjoys logical reasoning and uh English a lot and they score also well very good will do it we'll make sure that no stone is left Unturned great great so stress sir acting like physics teacher maths teacher logical teacher English teacher and how many students are on the channel wow so many I think I will teach more more subjects than the number of students watching now guys you should get your friends know how will I get motivated then you should get your friends also on the Channel Hannah you should make the channel popular yep very good very good make it angular velocity of the second hand angular velocity of the second hand of the watch guys Omega is 2 pi by time period because it is second hand one second hand will complete one revolution in one minute one minute means 60 seconds so it will become Pi by 30 that's all option b very good very good C it is option b only that's its simple formula our hand will take one hour right our hand oh sorry not RN my word minute hand will take one hour so that will be 60 into 60. our hand will take 12 hours for completing on the revolution so each one has a different angular speed okay there is a body which gives out energy at 5 Watts at 127 if the temperature is increased what will be the new rate I think it is based on Stephen bullsman law remember the rate at which radiation occurs the rate at which a radiation occurs is given by E Sigma a temperature raised to 4. so basically that power of radiation is directly proportional to the temperature's fourth power if you notice carefully 127 degree Celsius is how much guys 127 degree Celsius is how much guys it is 400 Kelvin always convert in kelvin else you will make a mistake and 927 degree Celsius is 1200 Kelvin very good now can you see from 400 to 1200 how many times has it increased from 400 to 1200 how many times does the temperature increased 400 threes are 1200 so it became three times it became three times so if temperature becomes three times three times raised to 4 3 into 3 into 3 into 3 how much will it be basically 81 times so basically the power radiated will become 81 times so that new radiated power will become 81 into 5 which is 405 Watts 405 Watts exactly so option C should be correct yes it is option C is the correct answer beautiful understood how we did it logically don't have to divide and then do it it is one and the same thing you don't have to sit and divide and take the ratios okay now there is a substance it becomes 1 16 of its original Mass into what is the half life time of that object radioactivity it has become 1 16 the moment you look at that number 1 by 16 you know it is a power of 2 and power of two is work really well for Half-Life questions correct 1 by 16 is 1 by 2 raised to 4 so basically 1 by 2 into 1 by 2 into 1 by 2 into 1 by 2. basically there were four Half Lives each half life if it is T half into 4 is the total time which is basically two hours is basically two hours so what is that Half-Life it is 2 divided by 4 which is half an hour which is 30 minutes of course 30 minutes which is option C exactly Janet very good yes that's the correct answer everybody with me so there are five half-lives five into Half-Life will be the total time that's how it works simple always powers of 2 helps a lot okay next question coming up on your screen the masters of two objects are 25 and 81 grams the kinetic energies are same then what is the ratio of the momentum how is momentum related to kinetic energy you know that kinetic energy is the square of momentum by 2m rather momentum is root of 2 times mass times the energy kinetic energy this is the formula so therefore P1 by P2 will be okay 2 2 will cancel masses will only come M1 by M2 K1 and K2 are same remember it is clearly mentioned kinetic energies are same so K1 is equal to K2 so don't bother writing it what is the mass 1 25 what is the mass 2 it is 81 root 25 5 root 81 9 so 5 by 9 should be the answer which is option C yes 5 by 9 very good so just using momentum square is 2 sorry momentum is root to MK we get the answer okay simple many students might find a reverse answer and you will wrongly Mark as 9 is to 5 you will definitely get negative 1. so be very careful for ratio questions because if you find the opposite ratio you will lose your marks okay incline plane in a lift which is moving down with retardation crazy guys so let me just show a lift you will understand what exactly is happening this is a lift which is going down and the speed is reducing guys so tell me one thing if a lift is going down it's clearly mentioned lift is going down with the retardation what does it mean where is it accelerating lift is going down and slowly stopping that means it is accelerating upwards now everybody agrees the acceleration is upwards agree or no very good now whenever the acceleration is up whatever happens inside the lift you will use whatever happens inside the lift you will use the value of the effective gravity as G plus a you will use the effective gravity as G plus a correct now inside the lift what is there there is a inclination there is an inclination there is Theta there is some block and that block is basically going to slide down what will be the acceleration of that block what will be the acceleration of the block which is basically sliding that block which is there which is sliding over here what do you think that acceleration will be that acceleration will be that effective gravity is sine Theta the total gravity which is perceived inside the left sine Theta y it is plus a remember if acceleration is up plus up is plus down is minus that's the trick don't waste your time G or sorry acceleration upwards positive acceleration downward is negative okay for these lift problems so it will basically become G plus a sine Theta now the last thing to be done is use kinematic equations guys let's use kinematic equations so using kinematic which equation I think s is u t plus half a d square u t plus half a t Square s is L initial speed 0 acceleration is G plus a into sine Theta time is T so that's it so basically it will become 2 L is equal to g plus a sine Theta into T Square so T will be equal to 2L divided by G plus a into sine Theta but because it was Square I am taking root so that will be the answer where is that option guys where is that option can you see it G plus a yes option A only correct very good proud of all of you if you've done this question good this will be a good level question it will take you more than one minute I told you there will be very few questions which will take you more than one minute and if you know the trick tuck tuck with steps you will do it else you will waste a lot of time if you think this question is hard leave it in the exam move to the next question don't waste your time on this question because it has kinematics it has Newton's laws and lift concept which is pseudo Force next one block is going up an incline plane speed is 5 it stops what is the coefficient of friction let's draw the free body diagram we'll get an idea the block is basically going up moving up velocity is up but acceleration will be opposite remember there will be normal force there will be mg cos Theta Force but that is not relevant to me I will have one force which is pulling it down and that is basically it's m g sine Theta component the normal and the mg cos is not going to matter so much okay and there will be also frictional force frictional force which will be mu m g cos Theta standard mu n n is mg cos Theta because of because of this force and this Force both these forces are decelerating the block so the deceleration will be in this direction or acceleration will be in this direction it is decelerating while moving forward so therefore I can just say looking at this okay mg sine Theta Plus mu mg cos Theta is equal to M into a mmm cancels G comes common so g into sine theta plus mu cos Theta is equal to a now why do I need this acceleration because I know it stops after some time so I think we'll have to use kinematic equation also so velocity is given it stops time is given so I think I will use final velocity is initial velocity plus acceleration into time final velocity 0 initial velocity how much is it 5. acceleration is negative because it is decelerating so minus g into sine Theta that means sine 30 plus mu cos 30 into time what is time 0.5 seconds time is basically 0.5 seconds so I'm just writing it over here okay everybody cool now just move these things around so it will become 0.5 into g g is basically 10 sine 30 is half uh plus mu root 3 by 2 is equal to 5. 5 into 10 is 5 this 5 and this 5 will get canceled and that 2 also I can take it outside so 1 by 2 outside 1 plus mu root 3 is equal to 1 so 1 plus mu root 3 is equal to 2 mu root 3 will then be 2 minus 1 which is 1 so mu will be 1 by root 3 which is basically 1 by 1.732 so how much will it approximately come out to be I think that value of mu will come close to 0.6 will come close to 0.6 you can do the math and see yes it is 0.6 okay everybody so again this question slightly lengthy but do ever a lot of steps are there but see it is viewable it will take some time and remember in the exam if you feel like leaving this question you can leave it but remember many people will leave this question even this question which I told you will many people will leave it if you want the top most Branch topmost bets obviously you will have to do this if you want computer science in bits pilani okay moving on to the next question guys coming up on your screen a planet of masam goes around the Sun elliptical orbit maximum and minimum distance are given what is the time period question on Kepler's loss guys so let's just draw an elliptical orbit just to get a hang of it okay again it has become tilted it's okay so just imagine I draw this I also so show the Sun okay this is where the sun is right and that planet will be going around it like that okay so this is how it is now it is mentioned in that particular question that the minimum and maximum and minimum are R1 and R2 so maximum is R1 minimum is R2 what is the time period proportional to by Kepler's Law by Kepler's Law what do we know the square of the time period is proportional to the semi major length the semi major lengths Cube can you find out what is the semi major length over here that is the big diameter half of it so guys semi major what is semi major it is exactly this much so it will be R1 plus R2 is the total so only this much only this much that is semi major so remember 2A is R1 plus R2 so therefore a is R1 plus R2 divided by 2 that's it so therefore it is basically R1 plus R2 divided by 2 whole Cube that is square of time so time will be proportional to R1 plus R2 whole raised to 3 by 2 remember constants do not matter constants do not matter in proportionality so it is option b not option D what is r what is that r so it is even an invalid option D is invalid there is no variable only called R what is that meaning of r so that is why it is wrong semi major length remember in a ellipse there is a major length minor length semi measure semi minor half of the major is semi or internal half of minor is also semi minor okay cool can we proceed very nice moving on now the work required to form a bubble of volume v is uh W how much work will be required to make a bubble of volume 2v interesting bubble volume surface tension definitely and why is work required because of surface energy so work is basically area into surface tension let's say I call it as t area will be 4 Pi R square remember 4 Pi R square is the area but it's a bubble so it has inner and outer surface that is the common that is the common mistake which many students do so into two and into that surface tension okay so that is the work done in the first case now what will be the work done in the next case okay that new work done W Prime will be 4 Pi that new radius square into 2 into the surface tension now many people will relax our volume is doubled so radius will also be doubled did you also think that then you are wrong how will the volume doubling make the radius double guys think carefully volume is four by three pi r Cube so if volume is doubled then what will happen what will happen the radius will become cube root of 2 times more cube root because R Cube no no no it is not three times cube root of two times because cube root of twos cube is 2. yes be careful cube root 2 understood this understood this concept volume is readable radius will be cube root of 2 times more cube root of 2 basically means 2 raised to 1 by 3 times of R so put that 2 raised to 1 by 3 times of R so when you do that what will you get over here you will get 4 pi 4 Pi R square into 2 into T into 2 raised to 2 by 3 if you notice this part is exactly this part is exactly this part yes or no just check it out it's exactly this part so it is basically that old work isn't it basically that old work and 2 raised to 2 by 3 will just come over here so basically it is W into 2 square is 4 4 raised to 1 by 3 so basically it is W cube root of four fourth a four raised to 1 by 3 into W which is option a i s c s option A many of you said option b no that is wrong see where you went wrong made a blender somewhere no it is not option b crazy King it is option A guys lot of you are making silly mistake as you come towards the end initially you are giving the answers correctly slowly or giving wrong answers so this is again a common Trend that is the reason why you should be practicing full-fledged mock test so that you have that stamina you have the right mindset you do not lose focus the moment you lose focus silly mistakes that laziness kicks in you will feel like not doing the motion okay two Springs constant 1500 3000 stretch by the same Force they have potential energy and water ratio what is the formula for potential energy the formula for potential energy is half k x square but it is clearly mentioned in the question that their forces are same we know force is basically k x so I have an idea now I will do some magical manipulation what I am going to do I'll multiply denominator and numerator with K so it will become k x whole square and just divided by K what is the reason for doing that because I know the term inside the bracket is force so it will become Force Square by K Force the square by K I know now that the force is not changing only spring constants are different so that's why potential energy will change only because of that spring constant so my dear students you is inversely proportional to K so U1 by U2 will be K2 by K1 what is K2 K2 is basically uh 3000 K1 is 1500 zero zero zero zero so it basically becomes 2 is to one so option D should be the answer very good this everybody got yes option D is the correct answer got it so I have used this concept of KX being the force manipulated so that I get the desired result read the question carefully something will be same something will be different identify who is proportional to what next beautiful question on your screen now at 27 degree celsius kinetic energy is E1 temperature increase to 327 what is the new kinetic energy going to be first let me convert the temperature into Kelvin because never will use in gas laws temperatures are in Celsius you have in formulas you have to convert it into Kelvin 27 degree celsius means 300 Kelvin 327 degree celsius means how much guys how much Guys 600 Kelvin correct so from 300 Kelvin to 600 Kelvin how much is the temperature change how many times did it change think about it from 300 to 600 how many times did it change two times okay I'll keep it on the side now let's think energy energy of a gas is given by n c v t energy of a gas is ncvt change in energy is ncv delta T ncv delta T this is a common mistake which they say I was expecting many students to write root 2. guys it is wrong root 2 will not be the answer question is not on RMS speed or most probable speed energy energy is directly proportional to the temperature energy is basically directly proportional to temperature speed is proportional to the root two times so if temperature becomes 2 times obviously the energy will also become 2 times so what is the answer to E1 which is option C yes lot of people write the answer as root 2 because you are thinking about speed and also common mistakes guys avoid this I'm telling you you will go into bits you will not regret not getting a seat into IIT or top nit you will be so happy in life this is the best best private college in the country I'm telling you don't look for any other option you have to make it through okay the life is really cool so many clubs and uh you know very good crowd very nice crowd you will enjoy it you will be like sir what is this crowd sir I don't even see such crowd in college such nice your type crowd is there so you will find very good crowd in bits let me tell you that many of my students are in bits and all your type students only have gone okay so guys uh the next few questions are basically I think I have kept homework questions also uh okay I think there is one question left over here let's do that as well uh in the given figure capacitors are there question is uh what is the effective capacity tense all right yes you can go to visit bit Sal also okay so after this all the remaining questions are homework guys this is the last question I'll be doing all right so let's see how do we do this question the moment you see this kind of a setup remember this setup is a standard setup of wheatstone this is a standard setup of wheatstone bridge so remember this so actually speaking this is in this form if you rearrange the circuit this is standard you should remember this circuit I mean if you see the connections in this form always convert it into wheatstone that's it now we know that the middle resistor sorry capacitor is completely useless this is useless fellow right this is completely useless fellow so therefore you will see yes switched on yes so basically you will see this capacitor connected to this capacitor this capacitor connected to this capacitor and like this now each one of them is four four I think yeah four micro farad so if this is four this is four this is four this is four guys in wheatstone if all are equal now the effective is also the same thing only anyways you can do it and find it out because they are in series because they are in series okay so what will happen it will become C by 2 this is also in series so this will also become C by 2 4 by 2 is 2 this is also two so two micro farad parallel to 2 micro farad so two plus two will become 4 micro farad so that is the answer for micro farad which is option b of course exactly very good very good proud of all of you okay so I think this was the last question I've kept some homework questions you'll be getting the homework questions after some time in the telegram channel so make sure you join the telegram Channel yes don't forget to join it and yes subscribe to the channel because I'm going to conduct lots and lots of classes for all of you before bits we have to be very well prepared I'll train you for physics also maths also chemistry are already getting trained and the logical reasoning also and English also so four subjects I'm going to teach you okay so I deserve a like okay uh yeah I'm openly telling this I deserve a life for this and I deserve little bit more popularity guys uh I want more students coming on the channel and watching these sessions all right thank you so much for watching this and enjoy your day and please work hard struggle for these last few days that's it this struggle will be worth it okay bye bye this is Captain shreyas and I'm signing off hasta la vista thank you

Channel: Unacademy IIT JEE English

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Id: yETcBaBGBIM

Length: 59min 33sec (3573 seconds)

Published: Thu May 18 2023