How much work is done by a weight lifter when he holds a weight of $80 \,kg$ on his shoulders for two minutes?

$(a)$ Define potential energy. Write an expression for potential energy of an object of mass $m$ raised through a height $h$.
$(b)$ Find the energy possessed by an object of mass $10 \, kg$ when it is raised to a height of $6 \, m$ above the ground. (Given $g = 9.8 \, m s^{-2}$)

Justify,giving proper reasoning,whether the work done in the following case is positive or negative: Work done by the resistive force of air on a vibrating pendulum in bringing it to rest.

When a body falls freely towards the earth,then its total energy

$A$ body is falling from a height $h$. After it has fallen a height $\frac{h}{2}$,it will possess

$(a)$ What is meant by mechanical energy? State its two forms. State the law of conservation of energy. Give an example in which we observe a continuous change of one form of energy into another and vice-versa.
$(b)$ Calculate the amount of work required to stop a car of $1000 \, kg$ moving with a speed of $72 \, km \, h^{-1}$.