Question

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 1

• Suma is swimming in a pond. Suma is doing work as she is able to move herself by applying force with the movement of her arms and legs in the water. 

• A donkey is carrying a load on its back. Donkey is not doing any work (in the sense of physics) as the weight he is carrying (the direction of force) and displacement are perpendicular to each other. 

• A wind-mill is lifting water from a well. Wind mill is lifting water from a well and doing work against the gravity. 

• A green plant is carrying out photosynthesis. No force and displacement are present here, so work done is zero. 

• An engine is pulling a train. During the pulling a train, engine does the work against the friction, present between the railway track and wheels. 

• Food grains are getting dried in the sun. During the drying the grains, there is no force as well as displacement is present. So, no work is done. 

• A sailboat is moving due to wind energy. Work is done by the wind as it moves the sailboat towards the direction of the force (force of blowing air).