A ball of mass m is tied to a vertical (Cyclinder) post of radius R. The mass sl

Question

A ball of mass m is tied to a vertical (Cyclinder) post of radius R. The mass slides on a frictionless, horizontal surface. As the ball travels around the post the string wraps around the post, shortening the length. At t = 0s, its speed is V(initial) and the distance from the axis of rotation is r(initial). Assume the ball is a point particle when calculationg its inertial mass.

1. As the string wraps its way around the post, what quantities are preserved? Explain.

2. What is the angular momentum of the ball after the string has wrapped once around the post?   

Explanation / Answer

1. As there is no external torque So only angular momentum is preserved / As centripetaal and centrifugal forces pass through the centre so there is no external torque

2.As angular momentum is preserved

So final angular momentum = initial angular momentum = mV(R+r)

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