A body is moved along a closed loop. Is the work done in moving the body necessarily zero? If not, state the condition under which work done over a closed path is always zero.

Calculate the work done by a car against gravity in moving along a straight horizontal road. The mass of the car is 400 kg and the distance moved is 2m.

A body falls towards earth in air. Will its total mechanical energy be conserved during the fall? Justify.

In an elastic collision of two billiard balls, which of the following quantities remain conserved during the short time of collision of the balls (i.e., when they are in contact).

(a) Kinetic energy.

(b) Total linear momentum? Give reason for your answer in each case.

Calculate the power of a crane in watts, which lifts a mass of 100 kg to a height of 10 m in 20s.