- #1

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- Homework Statement
- A 65kg student is ice skating as shown. She is initially rotating at with an angular speed of 2.5rad/s with her arms straight out. At this time she can be modeled as a vertical and horizontal cylinder as shown.

She then brings her arms in, at which point she can be modeled as only a vertical cylinder with the properties shown.

The moment of inertia for the vertical cylinders spinning around their axes is I = 1/2mr2.

The moment of inertia for the horizontal cylinder spinning around it's center, perpendicular to it's axis is I = (1/12)md^2.

Determine all of the following moments of inertia, angular speeds and angular momenta relative to the axis of rotation.

- Relevant Equations
- arms

m = 6kg

d = 1.7m

core

m = 59kg

r = 0.18m

full body

m = 65kg

r = 0.18m

I have the moment of inertia for the core(initial) and full body(final) but my answer for the moment of inertia for the arms(initial) was incorrect.

Arms(initial) moment of inertia:(1/12)(6)(1.7^2)=1.445 this is incorrect for some reason

Core(initial) moment of inertia: .9558

Full Body(final): 1.053

I also have to find the angular velocity and I have done this correctly for the arms and core but I could not figure out how to find the angular velocity for the full body(final)

Arms: 2.5 rad/s

Core: 2.5 rad/s

Full Body(final): I don't think I can solve this without the arms initial moment of inertia

Angular Momentum

Arms: my moment of inertia was incorrect so this was as well

Core: 2.3895

Full Body(final): My moment of inertia for the arms was incorrect so this was as well but this was my work to attempt to find it.

(1.445+.9558)2.5 = (1.053)w

w = 5.699 this was wrong but i tried to solve it anyway

I need help with the initial moment of inertia for the arms.

Arms(initial) moment of inertia:(1/12)(6)(1.7^2)=1.445 this is incorrect for some reason

Core(initial) moment of inertia: .9558

Full Body(final): 1.053

I also have to find the angular velocity and I have done this correctly for the arms and core but I could not figure out how to find the angular velocity for the full body(final)

Arms: 2.5 rad/s

Core: 2.5 rad/s

Full Body(final): I don't think I can solve this without the arms initial moment of inertia

Angular Momentum

Arms: my moment of inertia was incorrect so this was as well

Core: 2.3895

Full Body(final): My moment of inertia for the arms was incorrect so this was as well but this was my work to attempt to find it.

(1.445+.9558)2.5 = (1.053)w

w = 5.699 this was wrong but i tried to solve it anyway

I need help with the initial moment of inertia for the arms.