Sunday, 25 September 2016

The right approach to tackle JEE problems of kinematics

A large number of you have asked me about my approach to solve various problems. The million dollar question to answer is - how to think?
It is really hard to explain the thinking methodology in a blog post and so, I thought it'd be a good idea to rather make a video about it. I believe that you learn when you see things happen and so, instead of giving generic 'tips', I have taken concrete examples of 3 problems on kinematics and converted them to a video in which I have explained the right approach to solve them.
The goal is to not teach you kinematics. The goal is to teach you how to hit the problem from the very basic fundamentals.




Link: The video is also available here

I hope it will help you. Feel free to comment on the video or on the blog post.
Also, I would request you guys to please bear with me because I am not a professional video maker :)

38 comments:

  1. You seem to feel that using components is some sort of dirty shortcut. Why do you think using algebra, which gives you the same answer except you lose the physics of the problem at hand, is better ?

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    1. Because physics is not always intuitive. For instance, in the last problem, I see a lot of people getting the answer to be v = u*cos(theta) by equating the components along the vertical direction.
      I think solving the problem and getting the correct answer is more important than applying all possible Physics you know and even then getting the wrong answer. Maths is the language of physics and you should use it as much as possible.

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    2. That's a good philosophy and I can appreciate that this method may make it easier to grasp for a lot of people. . My main gripe was with you treating the use of vector components (which is also grounded in maths) as some sort of trick. Sure, mathematics may be the language of physics (and do I love my math) but what physics gives you is insight and deeper understanding (there's a nice Feynman video on difference between physicists and mathematicians). Apart from that nice video. Thanks for the help.

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    3. I appreciate your comments. However, I think its worth emphasizing that at JEE level, you are really not supposed to be that stellar at Physics. JEE paper setters are the professors of IITs and JEE paper takers are students of class 12th. No research work is expected for JEE aspirants. The main aim of JEE is to ensure that you are a fast learner and you are able to get things done. The aim is to train you to be a fast learner once you are in college.
      If you are able to get things done using some trick, it is always appreciated. At the same time, I would like to mention that I didn't really portray any 'tricks' in the video. I have showed how to approach things by definition. For instance, I have emphasized on the fact that students should think of a particular distance as x and use the definition of velocity to relate that x.
      I feel that its a good idea to apply maths to solve a Physics problem because Physics is to be applied to understand the problem. Eventually, every physics problem is a mathematics problem that is meant to be of a specific domain.

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  3. I believe that the method used in the video is the only one that can solve this problem directly .....but even if other methods exist they must be similar to this.U can say this bcoz there is no physical law by which u can equate velocity vectors in the above examples.....Even if velocity they must be equated in any situations we must either use 1.dx/dt 2.integration of acceleration with time 3.conservation of linear momentum 4. conservation of angular momentum.


    IN example 2...u may apply conservation of angular momentum about centre of mass....since rod is uniform assume to equal masses 'm' attached at the ends, the initial angular momentum is zero,but after velocity 'u' is given to one mass, the other mass attains velocity 'v'....now applying conservation of angular momentum about centre of mass....we get.... 0=mvlsin(theta)/2+mulcos(180-theta)/2....which is v=ucot(theta).....angular momentum about centre of mass is mass multiplied with cross product of velocity and distance from centre of mass and in this case distance is l/2.

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    1. Thanks for the alternative suggestions :)

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  4. What about live q&a session.we really need that more than this
    If u got time now plz try to arrange it .thanks in adv

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    1. We will schedule it soon! I am trying to get more IITians on board that can help :)

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  5. Hello Aman,

    I wanted to ask that whether you did problem practise in a rough or you managed them somewhere.

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    1. I used to solve problems in a rough notebook, but I used to keep the notebooks safely in case I need to look back at some problem

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  6. Please can u dedicate a post for all shortcuts of all concepts that you have learned.

    Thanks in advance

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  7. Very helpful post ... Thanks Aman Bhaiya

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  8. Hey Aman,can you pls organise once more live Q/A session preferably after 9,coz last time the session was held during coaching hours,so was not able to attend it,which may be the problems for others also,so pls look into this.
    Thanks.

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    1. Akshunn, thanks for your feedback. We will conduct a poll about a time that suits all of the readers :)
      Meanwhile you can take a look at our new daily practice problems platform: https://jeedpp.herokuapp.com/

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  9. Hi Aman,your method of solving problems is excellent.Thanks.Well,I am a jee 2017 aspirant there are 5 months left for exams.I just wanted you to help me tackle chemistry(my weakness).It's not up to the mark mainly oragnic.I can manage inorganic and physical but how do I reach that advanced level?..

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    1. Hi Sahil, I have replied to your comment on the other post :)

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  10. Thank you,it was a very helpful video.

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    1. Welcome :)
      You can take a look at our new daily practice problems platform: https://jeedpp.herokuapp.com/

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  11. I still cant understand the 1st problem,you used d(theta)/dt =omega,why so,,thats not the angle light house is tracing,it is the angle made by the ray of light with the light house,it will be constant every time shouldnt its diff. Be 0

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    1. Hello bhaiya.I am 2018 jee aspirant ..And I want to know that how you managed to read ncerts while doing non schooling , for iitjee. How ncerts helped you ..I am also doing non schooling and I spend my whole non coaching day reading notes of Sir.and thus donot get any reason to read ncerts..
      I am in dilemma..Please reply...

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    2. Hello bhaiya.I am 2018 jee aspirant ..And I want to know that how you managed to read ncerts while doing non schooling , for iitjee. How ncerts helped you ..I am also doing non schooling and I spend my whole non coaching day reading notes of Sir.and thus donot get any reason to read ncerts..
      I am in dilemma..Please reply...

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    3. Sunny, here is the explanation:
      The angular velocity of a body is defined as the rate of change of the angle that one of the axes of the body makes with a fixed line. Here, the laser acts as the axis. I think you can watch the video once again to get a better grasp of the problem statement.

      I would also appreciate if you can take a look at our new daily practice platform: https://jeedpp.herokuapp.com/

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  12. wait a minute here,,,now i get it,,the ray of light is moving like hands of clock in the plane of my screen,not spinning like water sprinkler in 3d space,,oh so silly i am,,anyways thankyou

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  13. Please can u dedicate a post for all shortcuts of all concepts that you have learned.

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  14. Hey aman I have questions when should a person solve ie irodov suppose if I want to solve kinematics in it1) after completing chapter 2)after completing 11th 3)after completing whole mechanics which is best one and plz reply soon

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  16. Sorry for sending two times
    And reply me ASAP

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  17. what about Live Q/A session

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  18. Hello Aman,
    This method is good can you make another video on rotational dynamics as the good questions are asked from rotational dynamics

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  19. Hey aman,it was really nice video...BTW I wanted you to ask that I am a FIITJEEian and it's test series is badaas..its marking scheme is what afraid me? What should I do?

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  20. Hey aman,it was really nice video...BTW I wanted you to ask that I am a FIITJEEian and it's test series is badaas..its marking scheme is what afraid me? What should I do?

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  21. Hey aman,it was really nice video...BTW I wanted you to ask that I am a FIITJEEian and it's test series is badaas..its marking scheme is what afraid me? What should I do?

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  22. I am solving hs verma for physics presently in class 9 am i doing right?
    I go to fiitjee bhilai and they cover high level chapters like QUANTUM NUMBERS, SOLUTIONS IN CHEMISTRY AND HIGHER MECHANICS AND KINEMATICS IN PHYSICS AND HIGHER LEVEL OF GEOMETRY, ALGEBRA IN MATHEMATICS. I am comfortable in these subjects. Will it help me in future for JEE or lose me anything. How would it help me. PLEASE HELP ME AMAN SIR. I AM YOUR GREAT FOLLOWER.PLS HELP

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  23. Respected sir....some of the queries I really wanted to ask you
    1.would reading theory directly from resnick halliday be enough after ncert or hcv's theory is also necessary for an extraordinary rank?
    2.is there even a bit significant difference in the walker and krane versions theory wise.
    3.one of my relative who just finished his electrical engineering from IIT Bombay suggested me to complete the whole syllabus in first twelve months and rest for revision and advance level problem solving skill building. Would it be a good approach or I'll mess up things cuz the coaching will be going by 2yr plan
    (time isn't the obstacle... I'll be able to manage 5 hrs for both the plans
    The coaching one and the suggested one
    4.the final question..... I have heard some of the rumors that only the ones who have done a great foundation before 11th generally come under 50 ranks... If an aspirant has started from 11th would he still manage to be in the top 50

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