# Angular Momentum and Conservation of Angular Motion

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1. Apr 6, 2016

### Aarron Anderson

• OP has been reminded that they need to show their work when posting schoolwork questions
1. The problem statement, all variables and given/known data
How much torque is needed to change the speed of spinning rate of a 3.50 kg sphere with a radius of 7.50 m from 900. rpm to 200. rpm in 3.0 s? [-1924  -1.92 x 103 Nm]

2. Relevant equations
t = I * α
I = (2/5)mr^2
t = F * r

3. The attempt at a solution
just cant get a crack at it.

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2. Apr 6, 2016

### ramzerimar

Actually, it's very easy.
You really just have to calculate the moment of inertia and, after that, determine the angular acceleration needed to slow the spinning rate from 900 to 200 rpm. First, convert rpm to rads/s. Angular acceleration equals change in angular velocity divided by change in time. As you said, torque equals moment of inertia times angular acceleration. You will find << Answer deleted by Moderator >>

Last edited by a moderator: Apr 6, 2016