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A stone tied to string of length l is wh...

A stone tied to 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 velocity as it reaches a position, where the string is horizontal (`g` being acceleration due to gravity) is

A

`sqrt(u^2-2gL)`.

B

`sqrt(2gL)`

C

`sqrt(u^2-gL)`.

D

`sqrt(2(u^2-gL))`.

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