Look at the activites 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 drired in the Sun. (g) A saliboat is moving due to wind energy.

Explanation

(a) Suma is doin work as she moves (displaces) herself force with the movement of her arms and legs in the water.
(b) A donkey is not doing any work (in the technical sense) as the weight he is carrying (i.e., force) and the displacement are peerpendicualr to each other. However, he does work against frication between his hoofs and the ground. Further, work is also done by the donkey if he cllimbs up a mountain as in that case force and displacement are not perpendicualr to each other.
(c ) The kinetic energy of the wind is imparted to the wind mill which lifts water from the well. Thus, a wind -mill works against the force of gravity to lift water vertically upward. (d) Photosynthesis is the process by which green plants use Sun's energy to build up carbohydrate reserves. In this case, both force (F) and displacement (s) are zero and as such work done is zero.
(e ) When the engine pulls train, it does work (i) in pulling the train and (ii) against the force of friction between the wheels of the train and the railway track.
(f) When the food grains are dried in the sun, solar radiation tekes moisture out of the food grains. Since there is no foce (F) and no displacement (s) is involved in the process, work done is zero.
(g) The force, F exerted by the wind on the sailboat moves it through a distance (s) in its direction Hence, work is done by the wind energy in moving the sailboat.