What is a watt?

An object of mass $5\,kg$ falls from a height of $5\,m$ above the ground. The loss of potential energy of the mass is:

At what speed will a body of mass $1\, kg$ have a kinetic energy of $1\, J$ (in $, m/s$)?

$(i)$ Define power. Mention its $SI$ unit.
$(ii)$ $A$ boy of mass $50 \, kg$ runs up a staircase of $40$ steps in $8 \, s$. If the height of each step is $15 \, cm$,find his power. (Given,$g = 10 \, m \, s^{-2}$)

State whether the following statement is true or false:
When an arrow is released from a bow,potential energy changes into kinetic energy.

$(i)$ $A$ 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? $(g = 10\, m s^{-2})$