Work is done whenever the given 2 conditions are satisfied:

(i) A force acts on the body.

(ii) There's a displacement of the body by the applying of force in or opposite to the direction of force.

• While swimming, Suma applies a force to push the water backwards. Therefore, Suma swims within the forward direction caused by the forward reaction of water. Here, the force causes a displacement. Hence, work is done by Suma while swimming.
• Whereas carrying a load, the donkey should apply a force within the upward direction. But, displacement of the load is within the forward direction. Since, displacement is perpendicular to force, the work done is zero.
• A wind mill works against the gravity to elevate water. Hence, work is finished by the wind mill in lifting water from the well.
• During this case, there's no displacement of the leaves of the plant. Therefore, the work done is zero.
• An engine applies force to tug the train. This allow the train to move within the direction of force. Therefore, there's a displacement within the train in the same direction. Hence, work is finished by the engine on the train.

• In this case during the process of food grains getting dried in the sun, no work is done as food grains do not displace in the presence of solar energy.

• In this case wind energy applies a force on the sailboat to push it in a forward direction. Therefore, the displacement of the boat is along the direction of the force. Hence, the work is done by wind on the boat.