$A$ man weighing $50 \, kg$ lifts a weight of $30 \, kg$ to the top of a building $10 \, m$ high. Find the work done by him. (Take $g = 9.8 \, m s^{-2}$) (in $, J$)

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

State whether the following statement is true or false:
In order to get minimum work,the angle between force and displacement should be $90^{\circ}$.

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

Define power. Write the commercial unit and $SI$ unit of electrical energy. An electrical geyser of $1.5 \, kW$ works for $2$ hours. Find the electrical energy units consumed in a day.

The $CGS$ unit of work is: