(a) The earth, moving around the sun in a circular orbit, is acted upon by a force and hence work must be. done on the earth by the force. State whether the statement is correct or not. Give reasons for your answer.

(b) A coolie holding a heavy box is waiting at the bus stand for 15 minutes. How much work is done by him ?

© A man weighing 70 kg carries a weight of 10 kg on the top of a tower 100 m high. Calculate the work done by the man. (g = 10 m s^-2).

(a) No, work is done because the force acting on the earth and the displacement along the tangent are perpendicular to each other.

Since W = FS cos 0 and = 90°, therefore, cos 90° = 0 Hence, W = 0.

(b) Since coolie is applying force on the heavy box to hold it but there is no displacement of

the box. Therefore, work done by him is zero.

© F = (70 + 10) = 80 kg wt = 80 x 10 = 800 N

S = 100 m

W = F x S = 800 x 100 = 80000 J