A particle rests on the top of a hemisphere of radius R. The smallest horizontal velocity that must be imparted to the particle if it is to leave the hemisphere without sliding down is
$\sqrt{gR}$
$\sqrt{2gR}$
$\sqrt{3gR}$
$\sqrt{5gR}$
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A simple pendulum of mass m and length l stands in equilibrium in vertical position. The maximum horizontal velocity that should be given to the bob at the bottom so that it completes on revolution is