# U. Phys

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What is the angular momentum of a 3.7kg uniform cylindrical grinding wheel of radius 25cm when rotating at 1500rpm?

How much torque(in magnitude) is required to stop it in 5.0s?

Could you explain this in detail, I don't really understand torque and momentum well.

• U. Phys -

You need to separate linear motion from rotational.

mass kg...........momentofinertia kg*m^2

and finally, memorize this
tangential velocity on a curve= radius*ang velocity

ang momentum=I*w
(that is ang momentum is momentofinertia * angular velocity)
So you need I for a solid disk, make you a convenient card with common shapes..http://en.wikipedia.org/wiki/List_of_moments_of_inertia
Using thin disk model, I= mr^2/2

b) Torque= I*angacceleration= I*(wf-wi)/time= mr^2/2(-1500*2PI/60)

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