The figure shows two masses ' $m$ ' and ' $M$ ' connected by a light string that passes through ${ }_a$ small hole ' $O$ ' at the centre of the table. Mass ' $m$ ' is moved round in a horizontal circle with ' $O$ ' as the centre. The frequency with which ' $m$ ' should be revolved so that ' $M$ ' remains stationary is
( $\mathrm{g}=$ gravitational acceleration)

Radius of curved road is ' $R$ ', width of road is ' $b$ '. The outer edge of road is raised by ' $h$ ' with respect to inner edge so that a car with velocity ' $V$ ' can pass safe over it, then value of ' $h$ ' is ( $\mathrm{g}=$ acceleration due to gravity)
Two bodies of mass 10 kg and 5 kg are moving in concentric circular orbits of radii ' R ' and ' r ' respectively such that their periods are same. The ratio between their centripetal acceleration is
A car is driven on the banked road of radius of curvature 20 m with maximum safe speed. In order to increase its safety speed by $20 \%$, without changing the angle of banking, the increase in the radius of curvature will be [Assume friction is same on the road]