Question

A child runs in a line that is tangent to a stationary playground merry-go-round. As he passes the merry-go-round, he grabs hold of it and hangs on. How does the angular momentum of the system just before the "collision" compare to the angular momentum just after the "collision"?

a) His tangential speed is smaller b) His tangential speed is the same c)His tangential speed is larger d) There is no way to tell

Answer 1

initial angular momentum

Li = 0.5 M r^2 wi + mv r

final angular momentum

Lf = (0.5 M r^2 + mr^2) wf

using conservation of angular momentum

Lf = Li

wf = (0.5 M r^2 (v/r) + mvr) / (0.5 M r^2 + m r^2)

vf = v ( 0.5 M r + m r) / ( 0.5 Mr + mr)

vf = v

option (b) is correct

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