AIPMT | 2015Work, Power and EnergyHard

Question

A mass m moves in a circle on a smooth horizontal plane with velocity v0 at a radius R0. The mass is attached to a string which passes through a smooth hole in the plane as shown.
                                           
The tension in the string is increased gradually and finally m moves in a circle of radius . The final value of the kinetic energy is :-

Options

A.mv02
B.2mv02
C.mv02
D.mv02

Solution

Angular momentum remains Constant because of the torque of tension is zero
⇒ Li = Lf
⇒ mv0R = mv
⇒ v = 2v0
KEf = m (2v0)2 = 2mv02
hence option (2)

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