A bucket containing water is revolved in vertical circle of radius r. To prevent the water from falling down, the period of revolution required is ($g$ = gravitational acceleration)

In case of perfectly elastic collision,

The distance of the two planets A and B from the sun are '$r_A$' and '$r_B$' respectively such that $r_B = 100\, r_A$. The ratio of the speed of planet A to that of planet B is (both the planets are revolving around the sun)

A square frame of each side L is dipped in a soap solution and taken out, the force acting on the film formed is ( T = surface tension of soap solution)