A disc of radius 2 m and mass 100 kg rolls on a horizontal floor. Its centre of mass has speed of 20 cm/s. How much work is needed to stop it?

1. 1 J

2. 3 J

3. 30 J

4. 2 J

An object of mass 500 g initially at rest is acted upon by a variable force whose x-component varies with x in the manner shown. The velocities of the object at the points x = 8 m and x = 12 m would have the respective values of nearly:

1. 18 m/s and 24.4 m/s

2. 23 m/s and 24.4 m/s

3. 23 m/s and 20.5 m/s

4. 18 m/s and 20.5 m/s