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.

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

$A$ light body and a heavy body have the same kinetic energy. Which one will have the greater momentum?

When the speed of a moving object is doubled,its:

$(a)$ What is the commercial unit of energy? Give its relationship with the $SI$ unit of energy.
$(b)$ An electric bulb of $60 \,W$ is used for $10$ hours every day. How many units of electrical energy are consumed by this bulb in one day?

$(i)$ An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the total work done against the force of gravity and by the force of gravity on the object? Explain with proper mathematical expression.
$(ii)$ $A$ certain force acting on a $20 \, kg$ mass changes its velocity from $5 \, m s^{-1}$ to $2 \, m s^{-1}$. Calculate the work done by the force.