$(a)$ 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?
$(c)$ $A$ man weighing $70 \, kg$ carries a weight of $10 \, kg$ to the top of a tower $100 \, m$ high. Calculate the work done by the man. $(g = 10 \, m s^{-2})$

(N/A) No,the statement is incorrect. Work is not done because the gravitational force acting on the Earth (directed towards the Sun) and the displacement (along the tangent to the circular path) are perpendicular to each other,i.e.,$\theta = 90^{\circ}$. Since $W = F S \cos \theta$ and $\cos 90^{\circ} = 0$,the work done $W = 0$.
$(b)$ Since the coolie is applying force to hold the box but there is no displacement of the box $(S = 0)$,the work done by him is zero.
$(c)$ Total mass $m = 70 \, kg + 10 \, kg = 80 \, kg$. Force $F = m \times g = 80 \, kg \times 10 \, m s^{-2} = 800 \, N$. Displacement $S = 100 \, m$. Work done $W = F \times S = 800 \, N \times 100 \, m = 80,000 \, J$.