Calculate the amount of work done in moving a $50 \, kg$ mass through a distance of $10 \, m$ by applying a force of $100 \, N$. (in $, J$)

What is power? How do you differentiate kilowatt from kilowatt hour? The Jog Falls in Karnataka state are nearly $20 \, m$ high. $2000$ tonnes of water falls from it in a minute. Calculate the equivalent power if all this energy can be utilized? $(g = 10 \, m \, s^{-2})$

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? $(g = 10 \,m/s^2)$

Can any object have mechanical energy even if its momentum is zero? Explain.

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.

$(a)$ Name two forms of energy involved while a pendulum oscillates.
$(b)$ Show with the help of a diagram that when does each type of energy attain its maximum value.
$(c)$ How do these energies vary while the pendulum oscillates?
$(d)$ Name and state the law involved.