Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’. • Suma is swimming in a pond. • A donkey is carrying a load on its back. • A wind-mill is lifting water from a well. • A green plant is carrying out photosynthesis. • An engine is pulling a train. • Food grains are getting dried in the sun. • A sailboat is moving due to wind energy.

Work is done whenever the given conditions are satisfied:

1. A force acts on the body.
2. There is a displacement of the body by the application of force in or opposite to the direction of the force.
3. Both the angle between force and displacement is not 90degree.

(a) Suma is swimming in a pond.

While swimming, Suma applies a force to push the water backwards. Therefore, Suma swims in the forward direction caused by the forward reaction of water. Here, the force causes a displacement.

• Both the displacement and force are in the same direction, the work is done by Suma while swimming.

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

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. Thus, the angle between the force and displacement is 90degree.

• Since displacement is perpendicular to force, the work done is zero.

(c) A windmill is lifting water from a well.

A windmill works against the gravitational force to lift 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.

• Both the displacement and force are in the same direction, the work is done by the windmill.

(d) A green plant is carrying out photosynthesis

No force is required for the process of photosynthesis. The plant does not exert any force to move.

• No displacement or force acts here, thus no work is done.

(e) An engine is pulling a train.

An engine applies force to pull the train. This allows the train to move in the direction of the force. The direction is forward.

• Both the displacement and force are in the same direction, the work is done.

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

There is no force involved in the process of drying food grains in the sun and the grains do not move.

• No displacement or force acts here, thus no work is done.

(g) A sailboat is moving due to wind energy

Wind energy applies a force on the sailboat to push it in the forward direction. It is moving in a forward direction.

• Both the displacement and force are in the same direction, the work is done.