A boy of mass$18 \mathrm{kg}$  is running with a speed of $12 \mathrm{km}/\mathrm{hr}$. Find the kinetic energy possessed by the boy.

Given that the kinetic energy of an object is $100 \mathrm{J}$. If the mass of an object is $2 \mathrm{kg}$ then find its speed.

A stationary football is kicked by a player such that it attains a speed of $3 \mathrm{m}/\mathrm{s}$ just after the kick. Find the work done by the player on the ball if the mass of the ball is $100 \mathrm{g}$.

Find the work done in increasing the speed of a car from $18 \mathrm{km} {\mathrm{h}}^{-1}$ to $36 \mathrm{km} {\mathrm{h}}^{-1}$. Given, the mass of the car is $1000 \mathrm{kg}$.

Does the potential energy of spring increase when it is in the state of extension, and decrease when it is in the state of compression?

What is the force required to lift a book of mass? This force is required to overcome which force?

What happens to the potential energy if the height of a body is doubled?

Give two examples of (a) bodies possessing gravitational P.E. (b) bodies possessing elastic P.E.

Define potential energy. Derive an expression for it. On what factors does gravitational potential energy depends?