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

$(a)$ Define work done by a constant force on an object. Write an expression for the work done.
$(b)$ How much work will be done on an object by a force if the displacement of the object is zero?
$(c)$ What is the kinetic energy of an object? Write an expression for the kinetic energy of an object of mass $m$ moving with a speed $v$.

When a coil spring is compressed,the work is done on the spring. The elastic potential energy:

State whether the following statement is true or false:
When a body falls on the ground and stops,the principle of conservation of energy is violated.

$A$ boy pushes the wall in the class for five minutes but the wall does not move. Another boy pushes the chair from the front to the back side of the class. In which case,more work is done?

$A$ $1 \, kg$ mass has a kinetic energy of $1 \, J$ when its speed is: (in $, m/s$)