A hoop of radius 2 m weighs 100 kg. It rolls along a horizontal floor so that its centre of mass has a speed of `20 cm//s`. How much work has to be done to stop it?

The moment of inertia of a disc is 5 xx 10(-4) kg.m^(2) . It is rotating freely about a vertical axis passing through its centre at a speed of 40 rpm. A piece of wax of mass 20 g is attached at a distance of 8 cm from its centre. Calculate its new speed.

A solid sphere of mass 10 kg rolls on a flat surface with out slipping with a speed of 50 cm. s^(-1) . Calculate its energy.

Mass of a rod of length 4m is 3 kg. Its centre of gravity is 1.5 m from one of its ends. At the other end a mass of 8 kg is tied up. The rod is at a horizontal position. It is turned to a vertical position in such a way that the 8 kg mass goes to the top. What is the work done in changing the orientation of the rod ?