Question

A hemispherical shell of mass m and radius R is hinged at point O and placed
on a horizontal surface MN as shown in the figure.
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Answer 1

•The minimum speed u is not possible. •This is explained by the concept of torque.

•The torque acting on the body about the axis of rotation is given by,

Torque = r x F = rFsin(theta).

•So the impulsive torque here is zero as the distance r is zero(points from axis of rotation to the point where force acts). so the impact caused will be absorbed and the shell does not move. •Hence no torque acts on the shell and therefore the answer is (D) not possible.