# Angular Momentum and Conservation of Angular Motion

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## Homework Statement

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]

t = I * α
I = (2/5)mr^2
t = F * r

## The Attempt at a Solution

just cant get a crack at it.[/B]

#### Attachments

• AP1 Unit10 Rotation - WS5 Angular Momentum.pdf
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## Homework Statement

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]

t = I * α
I = (2/5)mr^2
t = F * r

## The Attempt at a Solution

just cant get a crack at it.[/B]
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 >>

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