For each of the following scenarios, state whether the work done by gravity is positive, negative, or zero.
(a) A person walks on a levelled road.
(b) A person climbs a ladder.
(c) A car in a neutral gear is coming down the slope.
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(a) Zero
(b) Negative
(c) Positive
Reason —
(a) Zero because when a person walks on a levelled road, no work is done against the force of gravity as the displacement of the person is normal to the direction of force of gravity which is vertically downwards.
(b) Negative because when a person climbs a ladder (upward), the displacement covered by the person is opposite to the direction of force of gravity (downwards), so the work done on the person by the force of gravity is negative.
(c) Positive because when a car in neutral gear is coming down the slope, the direction of displacement covered by it has some angle θ with the direction of force of gravity (downwards) such that 0° ≤ θ < 90°, so the work done on the car by the force of gravity is positive.