Question

Question 1 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.

Class 9 - Science - Work and Energy Page 158

Answer 1

1. Suma is doing work by pushing water in the backward direction.

2. Force exerted by donkey in the upward direction is perpendicular to the horizontal displacement of the load. Therefore, no work is done.

3.Work is done in lifting water from the well against the force of gravity.

4.The leaves of plants remain at rest during photosynthesis.So,no work is done.

5.The engine is doing work in pulling the train and also both the applied force and displacement are in same direction.

6.As food grains remain at rest, so no work is done.

7.Work is done by the wind in moving the sailboat.

Answer 2

Hello!
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Here is your answer
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Work is done when:

# Force acts on a body

# There is a displacement of the body by application of force in or opposite to direction of force

Thus, based on that:

1) Work is done by Seema while swimming

2) Since displacement is perpendicular to force, no work is done by the donkey.

3) Work is done by a wind mill is lifting water from a well. 

4) The work done is zero, as there is no displacement of the leaves.

5) Work is done by an engine is pulling a train.

6) Food grains don't move, thus there is no work done.

7) Work is done by the boat.
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HOPE THIS HELPS YOU :)