How much work is done by a weight lifter when he holds a weight of $80 \,kg$ on his shoulders for two minutes?

The velocity of a body moving in a straight line is increased by applying a constant force $F$, for some distance in the direction of the motion. Prove that the increase in the kinetic energy of the body is equal to the work done by the force on the body.

State whether the following statement is true or false:
Work done by centripetal force is zero.

$A$ light and a heavy body have the same momentum. Which one will have greater kinetic energy?

Mountain roads rarely go straight up but wind up gradually. Why?

$(a)$ State the law of conservation of energy.
$(b)$ Establish the relation between the $SI$ unit of energy and the commercial unit of energy.
$(c)$ $A$ toy car is displaced through $5 \, m$ on the application of a force of $7 \, N$. Assuming the force acts on the object throughout the displacement,what is the work done in this case?