A stone is tied to a string of length $L$ 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 at 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 stone is tied to a string of length $L$ 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 at 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
$u-\sqrt{u^{2}-2 g l}$
- B
$\sqrt {2gL}$
- C
$\sqrt {{u^2} - gL}$
- D
$\sqrt {2({u^2} - gL)} $
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