# Complex motion part 2

1.A solid cone of length $h$ and half angle $\alpha$ is rolling on a plane about its vortex with an angular velocity of $\Omega\hat{k}$, as shown in Fig. Compute the angular velocity, angular momentum, and kinetic energy of the cone. 2. The vertex of the aforementioned cone is fixed on the $z$ axis at a height equal to the radius of the cone. The cone rotates an angular velocity of $\Omega\hat{k}$ about the vertical axis as shown in Fig. Compute the angular velocity, angular momentum, and kinetic energy of the cone.

Note by Azimuddin Sheikh
7 months, 1 week ago

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Here is my attempt at the second one. There are two rotations to consider:

1) The rotation of the cone about its own axis
2) The rotation of the cone about the vertical axis

Let $H$ be the height of the cone, $R$ be the radius of the cone, and $\alpha$ be the semi-angle.

$tan \, \alpha = \frac{R}{H} \\ H = \frac{R}{tan \, \alpha}$

Let the angular speed of the cone with respect to the vertical axis be $\omega$, and the angular speed of the cone with respect to its own axis be $\omega'$. They are related as follows (assuming no slipping):

$H \, \omega = R \, \omega'$

Let $I$ and $I'$ be the moments of inertia with respect to the vertical axis and the cone axis, respectively.

$I = \frac{3}{20} \, M \, (R^2 + 4 H^2) \\ I' = \frac{3}{10} \, M \, R^2$

The kinetic energy is then (angular momentum is similar):

$E = \frac{1}{2} I \, \omega^2 + \frac{1}{2} I' \, \omega'^2 \\ \frac{3}{40} \, M \, (R^2 + 4 H^2) \, \omega^2 + \frac{3}{20} \, M \, R^2 \, \omega'^2 \\ = \frac{3}{40} \, M \, R^2 \, \Big( 1 + \frac{4}{tan^2 \, \alpha} \Big) \, \omega^2 + \frac{3}{20} \, M \, R^2 \, \frac{1}{tan^2 \, \alpha} \, \omega^2 \\ = \frac{3}{40} \, M \, R^2 \, \omega^2 + \frac{9}{20} \, M \, R^2 \, \frac{1}{tan^2 \, \alpha} \, \omega^2$

- 7 months, 1 week ago

Thx @Steven Chase sir got.it.(How to.solve first one any ideas ? As such axis of rotation would.be at an angle.from angular.momentum vector right )??

- 7 months, 1 week ago

I'll start thinking about the first one. Did I get the second one right?

- 7 months, 1 week ago

Yes u r right @Steven Chase Sir ( David morin has the first part of the problem in it , but I dont know how they approach the question) . ( they confused me by adding angular momentums )

- 7 months, 1 week ago

Can you post the energy expression for the first part, so I can check my answer when I have it?

- 7 months, 1 week ago

@Steven Chase sir pls share how ur way of solving these 2 problem ? @Aaghaz Mahajan bro pls help u also ?

- 7 months, 1 week ago

Do you know the answers? I think the second one should be fairly easy. The first one will take a bit more work.

- 7 months, 1 week ago

@Steven Chase sir, Can u solve for second part and later first part sir? (Yes I know answers for second part .)

- 7 months, 1 week ago

Ok, I'll do the second part for now

- 7 months, 1 week ago