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 doing work. This is because Suma is moving herself in water of the swimming pool by applying force.
(b) A donkey is not doing work against gravity. This is because it is carrying load (weight) at right angles to the force of gravity. A donkey, however, does work against friction and air resistance.
(c) A wind-mill is doing work. This is because it is lifting up water from the well against the force of gravity.
(d) A green plant does no work during photosynthesis. This is because in this case both, the force as well as the distance moved are zero.
(e) An engine does work in pulling a train. This is because an engine applies force due to which the train moves.
(f) No work is done when food-grains are dried in the sun. This is because no force is applied and no motion takes place.
(g) Work is done when sailboat moves. This is because wind is applying force which produces motion in the sailboat.