Answer:
(i)
Suma is swimming in a pond: In this case, Suma pushes the water in the backward
direction. It is known as action. However, due opposite to reaction, the water
pushes the person in the forward direction. In this situation, the force and
the displacement are in the same direction. The work is done by Suma and the
work done by the force is positive.
(ii) A donkey is carrying a load on its back: If the displacement of an
object is perpendicular to the force acting on it, the work done by the force
on the object is zero.
In the given situation, the force of gravity on the load
is in the downward direction, whereas the displacement is in the horizontal
direction, i.e., the force and the displacement are perpendicular to each
other. There is no displacement in the direction of the force of gravity, and
therefore, work done is zero.
(iii) A wind-mill is lifting water from a well: In this
situation, the object (bucket of water from a well) moves upwards. The force exerted
by wind-mill is in the direction of displacement. Therefore, work is done. This
work done is positive as the force and the displacement are in same
direction.
(iv) A green plant is carrying out photosynthesis: Since
there is no force applied or displacement, no work is done in this case.
(v) An engine is pulling a train: In this situation, an
engine is pulling a train parallel to the ground. The force exerted by the
engine is in the direction of displacement of the train. Thus, the force and
the displacement are in the same direction. Therefore, work is done. This work
done is positive.
(vi) Food grains are getting dried in the Sun: Since there
is no displacement, no work is done in this case.
(vii) A sailboat is moving due to wind energy: The force
exerted by wind on the sail moves the boat in the direction of force, hence,
positive work is done by wind energy.
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