JEE 2011:



Here's one concept that was highlighted in the paper. Literally, people (including me) fought over the validity of the problem. (Q 33, Paper 1).

Lets not get into the problem. Instead, lets do something simpler.

The vertical black rod is mass-less. The blue rod has mass 'm'. The vertical rod is rotated at an angular velocity 'w'. Calculate the kinetic energy of the system for two cases:

1)Blue rod is free to rotate about 'A'. ('A' is then called a 'hinge' joint).
2)Blue rod is not allowed to rotate about point 'A'.

P.S. Hope the blog readers did well!

14 comments:

  1. ShivankerApril 11, 2011 at 9:41 PM

    Acc. to me..
    K(a)= 1/2 m.w^2.L^2
    K(b)= 1/2 m.w^2.L^2 + 1/2(m.a^2/12)w^2

    but i messed up the question in the exam!

    ReplyDelete
  2. ShivankerApril 11, 2011 at 9:47 PM

    even the solution wasn't clear to me.. but after seeing this question.. i think i got it.
    Thanx bhaiya!
    Hope m correct here...

    ReplyDelete
  3. AnujApril 11, 2011 at 11:13 PM

    1)We'll not discuss ppl's marks here.

    2)Your answer is right. But the important thing is to visualize the motion of the blue rod.

    ReplyDelete
  4. Sambhav GuptaApril 12, 2011 at 12:49 AM

    ppr k time bhi galat kia tha, and abhi bhi samajh nhi aaya

    why is omega of com of rod about hinging point same as omega of rod about com?

    ReplyDelete
  5. mayankApril 12, 2011 at 9:17 AM

    bhaiya, please explain the motion of the rod. Couldn't get it!

    ReplyDelete
  6. shaanApril 12, 2011 at 10:47 AM

    sambhav, just try to visualise, jab rod move hi nhi kari abt hinge, toh w[rod]=w, taking wall ka hinge as centre

    ReplyDelete
  7. Pulkit MendirattaApril 12, 2011 at 12:05 PM

    hey, please clear.
    according to my visualisation, the answer shivanker gave to (a) should be for (b) and vice-versa.
    I mean in (b) part, it isnt allowed to rotate.
    please clear this

    ReplyDelete
  8. Sambhav GuptaApril 12, 2011 at 1:03 PM

    ok i got the motion now, good question by jee!

    ReplyDelete
  9. AnujApril 12, 2011 at 1:29 PM

    Hi Pulkit,
    Shivanker's answer is right. Try once again.

    ReplyDelete
  10. mayankApril 12, 2011 at 2:13 PM

    hey please explain the motion to me also.thanx

    ReplyDelete
  11. mayankApril 12, 2011 at 2:16 PM

    And first of all make me clear motion is like a pendulum or what?

    ReplyDelete
  12. AnujApril 12, 2011 at 11:13 PM

    have 11th class students (now 12th) done summation of series?

    ReplyDelete
  13. Sambhav GuptaApril 13, 2011 at 2:56 AM

    yes they must have, this is the time we did conics/calculus

    ReplyDelete
  14. Pulkit MendirattaApril 14, 2011 at 7:14 PM

    yes, we have done it.(2012 batch)

    ReplyDelete

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