Question

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?

Answer 1

Radius of the hoop, r = 2 m
Mass of the hoop, m = 100 kg
Velocity of the hoop, v = 20 cm/s = 0.2 m/s
Total energy of the hoop = Translational KE + Rotational KE

Moment of inertia of the hoop about its centre, I = mr²

The work required to be done for stopping the hoop is equal to the total energy of the hoop.

Required work to be done, W = mv² = 100 × (0.2)² = 4 J