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# Physics help! Momentum?

A 20 kg child is sitting on the outer edge of a 90 kg carousel with a radius of 3.0 m. (the carousel can be seen as a disk, child can be seen as point mass). The carousel is initially at rest.

a) What is the moment of inertia of the carousel and child?

b) The child pushes against the ground with a force of 25 N to get the carousel moving. What is the resulting torque?

c) What is the angular acceleration of the carousel and child?

d) What is the kinetic energy of the child and carousel after 10 s?

Please help!

### 1 Answer

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- SteveLv 79 years agoFavorite Answer
a) I = ½*90*3.0² + 20*3² = 585 kg∙m²

b) Q = F*R = 25*3 = 75 N∙m

c) α = Q/I = 75/585 = 0.1282 rad/sec²

d) KE10 = ½Iw² = ½I*(α*t)² = ½*585*(0.1282*10)² = 480.77 J

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