Question

In the following case, state whether work is done or not. Justify your answer. 1) A student reads a book. 2)The revolution of earth around the sun.

Answer 1

1) When a student reads a book no work is done because there is no displacement.
2) No work is done when the earth revolt around the sun because the work done in a circular motion is zero.

Answer 2

Hey dear,

◆ Work done -
Work done is dot product of force and dispacement.
W = F.d
W = Fdcosθ

◆ For given conditions -
1. When student is reading a book, displacement is zero, hence work done is zero.
As d = 0 ,
Hence W = 0

2. When earth revolves around the sun, instantaneous displacement is tangential and centripetal force along radius of revolution, thus work done is zero.
Here, θ = 90°, cosθ = 0,
Hence, W = 0

Hope this helps you...