Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work'.

(a) Suma is swimming in a pond.

(b) A donkey is carrying a load on its back.

(c) A wind-mill is lifting water from a well.

(d) A green plant is carrying out photosynthesis.

(e) An engine is pulling a train.

(f) Food grains are getting dried in the sun.

(g) A sailboat is moving due to wind energy.

Work is said to be done when force applied on an object shows the displacement in that object.

(a) While swimming, Suma applies a force to push the water backwards. She swims in the forward direction caused by the forward reaction of water. Here, the force causes a displacement. Hence, the work is done.

(b) While carrying a load, the donkey has to apply a force in the upward direction. But, displacement of the load is in the forward direction. Since displacement is perpendicular to force, the work done is zero.

(c) A windmill works against gravity to elevate water. The windmill lift water by applying a force in an upward direction, and thus the water is moving in the same upward direction itself. Hence, work is done.

(d) No force is required when a green plant is carrying out photosynthesis and there is no displacement of plant. Hence, no work is done.

(e) When an engine is pulling a train, it is applying a force in the forward direction and the train is moving. As, displacement and force are in the same direction. Hence, work is done.

(f) As there is no force applied when grains are dried and there is no displacement as well. Hence, no work is done.

(g) When a sailboat is moving due to wind energy, it is applying force in the forward direction. So, it is moving in the forward direction. As, displacement and force are in the same direction. Hence, work is done.