Circular Motion

A body initially at rest and sliding along a frictionless track from a height＇$h$＇（as shown in figure） just completes a vertical circle of diameter $\mathrm{AB}=d$ ．The height＇$h$＇is equal to

A particle of mass $m$ is suspended from a point O by a string of length $R$ ．It is given a velocity $u=3 \sqrt{g R}$ at the bottom．The difference in tension at point $B$ and at the point $C$ is $m$

A pellet of mass 1 g is moving with an angular velocity of 1 rad/s along a circle of radius 1 m. The centrifugal force is