Consider the following statements. Work is not done, when:
1. a man is walking on a horizontal road.
2. a man is climbing up a hill.
3. a man with a load on his head is walking on a horizontal road.
4. moon is revolving round the earth.
Which of the statements given above are correct?

Options

A. 1 and 3 only
B. 1 and 4 only
C. 2, 3 and 4
D. 1, 3 and 4

Answer

D

Explanation

Work done is given by, w = F s cos `theta`
where `theta` is the angle between the directions of force applied and displacement.
In cases 1 and 3, `theta=0`
`therefore` work done = 0
In case 2, w = f s cos 0 = mgh, h being height covered.
In case 4, force is always perpendicular to motion i.e., `theta = 90^@`, hence w = 0