The $CGS$ unit of work is:

An object of mass $40 \text{ kg}$ is pulled up to a height of $0.5 \text{ m}$. Calculate the work done. (Given $g = 9.8 \text{ m s}^{-2}$) (in $J$)

$(a)$ How much work is done when a force of $1\, N$ moves a body through a distance of $1\, m$ in its direction?
$(b)$ Is it possible that a force is acting on a body but still the work done is zero? Explain giving one example.

$(i)$ $A$ light and a heavy object have the same momentum. What is the ratio of their kinetic energies? Which one has a larger kinetic energy?
$(ii)$ $A$ ball is dropped from a height of $10\, m$. If the energy of the ball reduces by $40\%$ after striking the ground,how high can the ball bounce back? $(g = 10\, m s^{-2})$

State the energy conversions in a dry cell.

$(a)$ Name two forms of energy involved while a pendulum oscillates.
$(b)$ Show with the help of a diagram that when does each type of energy attain its maximum value.
$(c)$ How do these energies vary while the pendulum oscillates?
$(d)$ Name and state the law involved.