Answer :

(a.) Work done by the boy on the ladder = 0 J

All the work done by the boy in climbing up the ladder is done against gravity. His displacement with respect to the horizontal is zero.


(b.) Weight of the boy = 200 N


Frictional force = (3/10) of the weight of the boy


= 60 N


Work done by frictional force = Frictional force × Length of the ladder × cosθ


(where θ = angle between force of friction and displacement of the boy as he comes down)


= 60 × 10 × cos180°


= -600 J


(c.) Work done in this case is done against gravity = Weight of the boy × height of the ladder


= 200 × 8


= 1600 J


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