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

Work will be done if a force acts on an object and displacement occurs in the direction of force. According to this explanation work is done in following activities:
• Suma is swimming in a pond.
• A donkey is carrying a load on its back.
• A windmill is lifting water from a well.
• An engine is pulling a train.
• A sailboat is moving due to wind energy.

Answer 2

Work is performed when two conditions are met: 
→ A force acts on the object. 
→ The object experiences displacement due to the application of force either in the same direction or opposite to the force.

(a) Suma swims by exerting a force to push water backward, causing her to move forward due to the water's reaction. As the force causes displacement, work is done by Suma while swimming. 
(b) When a donkey carries a load, it exerts an upward force, but the load moves forward. Since the displacement is perpendicular to the force, no work is done. 
(c) A windmill lifts water against gravity, performing work to raise water from the well. 
(d) If plant leaves do not move, no displacement occurs, resulting in zero work done. 
(e) An engine pulls a train by applying force, causing the train to move in the same direction. As there is displacement, work is done by the engine on the train.
(f) Food grains remain stationary under solar energy, resulting in zero work during the drying process in the sun. 
(g) Wind energy propels a sailboat forward by applying force to it, leading to displacement in the boat's direction. Consequently, work is done by the wind on the boat.