A metre stick is pivoted about its centre. A | vedclass

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(C) According to the principle of conservation of angular momentum,the angular momentum of the wax about the pivot before the collision must be equal

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(C) According to the principle of conservation of angular momentum,the angular momentum of the wax about the pivot before the collision must be equal to the angular momentum of the system (stick + wax) after the collision.The angular momentum of the wax before the collision is given by $L = mvr$,where $m = 20 \,g = 0.02 \,kg$,$v = 5 \,m/s$,and $r = 0.5 \,m$ (since the stick is a metre stick and it is pivoted at the centre,the distance from the centre to the end is $0.5 \,m$).$L = 0.02 	imes 5 	imes 0.5 = 0.05 \,kg \cdot m^2/s$.The angular momentum of the system after the collision is $L = I\omega$,where $I = 0.02 \,kg \cdot m^2$ is the moment of inertia of the stick and wax about the pivot.Equating the two,we get $0.05 = 0.02 	imes \omega$.$\omega = \frac{0.05}{0.02} = 2.5 \,rad/s$.

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