What is elastic potential energy? Give some examples also.

Ratio of potential energies of body A and body B will be

A spring of spring constant $\mathrm{K}= 4\mathrm{x}{10}^3\mathrm{N}/\mathrm{m}$ is compressed by $2 \mathrm{cm}$, then determine the potential energy stored in spring. 

Give reasons for the following: An arrow moves forward when released from the stretched bow.

Give reason for the following:

Winding the spring of a toy car makes it run on the ground.

Give reason for the following: A bullet is released on firing the pistol.

Give reasons for the following: After winding the spring of watch, the hands of the watch move.

An object of mass $10 \mathrm{kg}$ is dropped from a height of $20 \mathrm{m}$. Calculate the potential energy and kinetic energy of the object at various heights as mentioned in the data:

Show by calculations that the above data verifies the law of conservation of energy. (take $\mathrm{g}=10 \mathrm{m}/{\mathrm{s}}^2$ )