Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term ‘work’:
(i) Suma is swimming in a pond.
(ii) A donkey is carrying a load on its back.
(iii) A wind mill is lifting water from a well.
(iv) A green plant is carrying out photosynthesis.
(v) An engine is pulling a train.
(vi) Food grains are getting dried in the sun.
(vii) A sailboat is moving due to wind energy.
(i) Yes, Suma is doing work by pushing water in the backward direction.
(ii) No, because the force exerted by donkey in the upward direction is perpendicular to the horizontal displacement of the load. Hence, no work is done.
(iii) Yes, work is done in lifting water against the force of gravity.
(iv) No, because the leaves of plants remain at rest during photosynthesis.
(v) Yes, engine is doing work in pulling the train. Both the applied force and displacement are in same direction.
(vi) No, because food grains remain at rest.
(vii) Yes, work is done by the wind in moving the sailboat.
Write an expression for the work done when a force is acting on an object in the direction of its displacement.
When do we say that work is done?
A pair of bullocks exerts a force of 140 N on a plough. The field being ploughed is 15 m long. How much work is done in ploughing the length of the field?
Define 1 Joule (J) of work.
