System Of Particles And Rotational Motion Ques 23

23. A mass $m$ moves in a circle on a smooth horizontal plane with velocity $v_0$ at a radius $R_0$. The mass is attached to 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 $\frac{R_0}{2}$. The final value of the kinetic energy is [2015]

(a) $\frac{1}{4} mv_0^{2}$

(b) $2 mv_0^{2}$

(c) $\frac{1}{2} mv_0^{2}$

(d) $mv_0^{2}$