Supplement


Find the moment of inertia of a hollow cone of mass M.. abt the axis shown..

Correct ans. on the first attempt only!

22 comments:

  1. do we have to consider the base of the cone...?

    ReplyDelete
  2. just to clarify.. the axis shown is the natural axis..or the axis passing thru the apex and perpendicular to the base..

    ReplyDelete
  3. i asked that stupid question cuz i m getting the same as vibhav...plz see to it..

    areal density=[M/{pi*R*sqrt(L^2+R^2)}

    area of one elemental ring=perimeter*width=(2*pi*x*tanQ)*(dx)

    apply the formula for the moment of inertia of a ring of radius x*tanQ
    then integrate from 0 to L

    at then end, substitute tanQ=R/L

    ReplyDelete
  4. i had a doubt with my answer as well.
    if L=0, it should give the MI of a ring which it doesnt.

    ReplyDelete
  5. mistake is in the 2nd step..area is NOT what you say it to be....keep on trying!

    also, at L=0, it gives the ans. of a disc, not a ring..

    ReplyDelete
  6. yeah. my bad.
    I made ditto same mistake.
    got the answer now though.
    sambhav, y dont u try converting height into radius and integrating from 0-R
    ull avoid the mistake then\and afterwards ponder wat u did wrong.

    ReplyDelete
  7. didn't get you....
    what is the answer?

    ReplyDelete
  8. that's for a solid cone yaar...

    ReplyDelete
  9. Sanchit got it right..Man! i thought it was simpler than Problem 5..

    ReplyDelete
  10. yess mr^2/2

    assume a small element dx, x height below the top.

    it will be a cylinder. dI=dm r^2

    find dm by taking S.A. ratio multiplied by total mass

    integrate. L^4 get cancelled

    ReplyDelete
  11. bhaiya mjhe meri galti kahan hai ye to pata lag gaya...par kya sahi lena tha yeh bata do..

    what would be the width of an elemental ring?

    ReplyDelete
  12. liquids ke sse1 me bhi to dx/cosQ liya hai

    ReplyDelete
  13. waise to its 2 late..but iv got it 2...

    ReplyDelete
  14. anuj bhaiya can u plz tell ur id wanna discuss something with u

    ReplyDelete
  15. shit man..!
    pehle dx lia...phir dx*secQ phir dx*tanQ
    secQ vale ko chodkar baki dono answers post kar die...

    ReplyDelete