In case of negative work,the angle between the force and displacement is: (in $^o$)

State whether the following statement is true or false:
Kilowatt hour $(kWh)$ is the unit of power.

$A$ ball is dropped from a height of $10 \, m$. If the energy of the ball reduces by $40 \%$ after striking the ground,how much high can the ball bounce back (in $, m$)? $(g = 10 \, m s^{-2})$

Four persons jointly lift a $250 \,kg$ box to a height of $1 \,m$ and hold it.
$(a)$ Calculate the work done by the persons in lifting the box.
$(b)$ How much work do they do just holding it?
$(c)$ Why do they get tired while holding it? $(g = 10 \,m/s^2)$

$(i)$ Define the term potential energy. Write the $SI$ unit of potential energy.
$(ii)$ $A$ body of mass $50 \, kg$ is situated at a height of $10 \, m$. What is its potential energy? (Given $g = 10 \, m s^{-2}$)

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