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# A ball of mass m is attached to one end of a light rod of length $l$, other end of which is hinged . What minimum velocity 'v' should be imparted to the ball downwards so that it can complete the circle

$(a)\;\sqrt {gl} \quad (b)\;\sqrt {5gl} \quad (c)\;\sqrt {3gl} \quad (d)\; \sqrt {2gl}$

+1 vote
The velocity at top most position of circle must be zero for finding minimum velocity of projection.
$v=0$
$v^2-u^2=-2gh$
$0=u^2-2gh\qquad (h=l)$
$u=\sqrt{2gl}$
Hence d is the correct answer.

edited Jul 25, 2014

+1 vote