question_answer 13)

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.  

Answer:

(a) Suma is doing work. She is applying force to move horizontally.   (b) Donkey is not doing any work. Here, the displacement and the force are at 90°.   (c) Work is done by the windmill. The water is lifted against force of gravity.   (d) No work is done by a green plant during photosynthesis.   (e) The engine applies a pulling force on the train, and the train moves in the direction of this force. Therefore, engine is doing work.   (f) During drying of food grains in the sun no work is done.   (g) Work is done by the air. The sailboat moves in the direction of the force exerted by wind.