A stone tied to a string $L$ is whirled in a vertical circle, with the other end of the string at the centre. At a certain instant of time, the stone is as its lowest position and has a speed $u$. the magnitude of the change in its velocity as it reaches a position where the string is horizontal is

  • A

    $\sqrt {{u^2} - 2gL} $

  • B

    $\sqrt {2gL} $

  • C

    $\sqrt {{u^2} - gL} $

  • D

    $\sqrt {2\left( {{u^2} - gL} \right)} $

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