A mass m moves in a circle on a smooth horizontal plane with velocity ${\mathrm{v}}_0$ at a radius ${\mathrm{R}}_0$. 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 $\frac{{\mathrm{R}}_0}{2}$
The final value of the kinetic energy is

• A

  ${{\text{mv}}^2}_0$

• B

  $\frac{1}{4}$${\mathrm{mv}}_0^2$

• C

  2 ${\mathrm{mv}}_0^2$

• D

  $\frac{1}{2}$${\mathrm{mv}}_0^2$