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A ball is hanging vertically by a light extensible string of length \( l \) from fixed point \( O \). The ball of mass \( m \) is given a speed \( u \) at the lowest position such that it completes a vertical circle with centre at \( O \) as shown. Let \( A B \) be a diameter of circular path of ball making an angle \( \theta \) with vertical as shown, ( \( g \) is acceleration due to gravity)
Let \( K_{A} \) and \( K_{B} \) be kinetic energy of ball when it is at \( A \) and \( B \) respectively, then \( K_{A}-K_{B} \) is equal to.
(1) \( 2 m g l \cos \theta \)
(2) \( 4 m g l \cos \theta \)
(3) \( m g l \cos \theta \)
(4) None of these
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