OK so this is about Moment of Inertia
http://grephysics.net/ans/9277/82
The correct answer is I=(1/3)Md^2
But let's analyze it as follows:
$$I=\int r^2\,dm=\lambda \int^d_{d} r^2\,dr=\dfrac{\lambda}{3} (d^3+d^3)$$
So finally we have:
$$I=\dfrac{2 \lambda d^3}{3}=\dfrac{2 M d^2}{3}$$
So there's a missing/additional factor of 2. Could you please tell me what I am missing ?
GR9277 #82
 HappyQuark
 Posts: 762
 Joined: Thu Apr 16, 2009 2:08 am
Re: GR9277 #82
In Yosun's original problem, she accidentally put an extra factor of 2 in the denominator of the answer that is supposed to be the correct one. Look at the original question from the booklet and you'll see what I mean.ali8 wrote:OK so this is about Moment of Inertia
http://grephysics.net/ans/9277/82
The correct answer is I=(1/3)Md^2
But let's analyze it as follows:
$$I=\int r^2\,dm=\lambda \int^d_{d} r^2\,dr=\dfrac{\lambda}{3} (d^3+d^3)$$
So finally we have:
$$I=\dfrac{2 \lambda d^3}{3}=\dfrac{2 M d^2}{3}$$
So there's a missing/additional factor of 2. Could you please tell me what I am missing ?
http://physicsgrad.com/pgre/927782

 Posts: 80
 Joined: Tue Oct 12, 2010 8:00 am
Re: GR9277 #82
$$\lambda = \frac{M}{2d}$$ali8 wrote:So there's a missing/additional factor of 2. Could you please tell me what I am missing ?
Re: GR9277 #82
@ HappyQuark: Thanks, but anyway my problem is only with Moment of Inertia regardless
of the angular frequency (i.e. the final answer).
@ physicsworks: Oh you are right, that was the problem!!
Thanks everybody, I guess on need to be superconcenterating in the real PGRE...
of the angular frequency (i.e. the final answer).
@ physicsworks: Oh you are right, that was the problem!!
Thanks everybody, I guess on need to be superconcenterating in the real PGRE...