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Question: A stone tied to a string of length L is whirled in a vertical circle with the other end of string at...

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

A

u2−2gL\sqrt { u ^ { 2 } - 2 g L }

B

C

D

Answer

u2−2gL\sqrt { u ^ { 2 } - 2 g L }

Explanation

Solution

Using conservation of energy

12\frac { 1 } { 2 } mv2 + mgL = 12\frac { 1 } { 2 } mu2

or v = u2−2gL\sqrt { u ^ { 2 } - 2 g L }