$A$ body of mass $5\, kg$ initially at rest is subjected to a force of $20\, N$. Find the kinetic energy acquired by the body at the end of $10\, s$. (in $, J$)

$A$ boy of mass $40 \, kg$ runs up a flight of $50$ steps,each $10 \, cm$ high,in $5 \, s$. Find: $(i)$ the work done by the boy,and $(ii)$ the power developed. $(g = 9.8 \, m s^{-2})$

$(a)$ Define the term 'average power'.
$(b)$ When a player hits a football,it moves along a curved path and then falls to the ground. Calculate the work done by the force of gravity on the football.
$(c)$ Two friends,Ram and Shyam,each having a mass of $40 \, kg$,go for rock climbing. Ram climbs to a height of $3 \, m$ in $10 \, s$ and Shyam covers the same height in $12 \, s$. Is the work done by Ram and Shyam equal or not? Compare the power of Ram and Shyam.

$A$ spring which has been kept compressed by tying its ends together is allowed to be dissolved in an acid. What happens to the potential energy of the spring?

State whether the following statement is true or false:
Work and energy have different units.

$(a)$ State the law of conservation of energy.
$(b)$ What is the work done to increase the velocity of a car from $36 \, km/h$ to $72 \, km/h$ if the mass of the car is $1500 \, kg$? Does the work done by the force have a negative or a positive magnitude?
$(c)$ Where does an oscillating pendulum have maximum potential energy $(PE)$ and kinetic energy $(KE)$?