A body of mass $m\, kg$ is rotating in a vertical circle at the end of a string of length $r$ metre. The difference in the kinetic energy at the top and the bottom of the circle is

  • A

    $\frac{{mg}}{r}$

  • B

    $\frac{{2mg}}{r}$

  • C

    $2mgr$

  • D

    $mgr$

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