(i) When a body is thrown upwards, gravity does the negative work. Since the gravitational force acts downwards but the displacement is upwards. (ii) When we walk frictional force does the negative work since frictional force acts opposite to displacement.

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Answer

Let, work done = W

We know,



Where,



= Force



= displacement

Let, θ = angle between

Then,



Work done is negative if,



If

So whenever force acts opposite to displacement work done is negative.

Examples of Negative work done are

(i) When a body is thrown upwards, gravity does the negative work. Since the gravitational force acts downwards but the displacement is upwards.

(ii) When we walk frictional force does the negative work since frictional force acts opposite to displacement.

(iii) For a liquid flowing, viscous force does the negative work since it acts opposite to the direction of the force.

(iv) On a see-saw, negative work is done since we apply the force downwards but the person is sitting opposite to us is displaced upwards.

(v) In the case when we pull out water from a well negative work is done since we pull the rope downwards but the bucket is displaced upwards

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