From a waterfall,water is pouring down at the rate of $100 \,kg/s$ on the blades of a turbine. If the height of the fall is $100 \,m$,the power delivered to the turbine is approximately equal to .......... $kW$.

$A$ car of mass $m$ is driven with acceleration $a$ along a straight road against a constant external resistance $R$. When the velocity is $v$,the power of the engine is

$A$ man is riding a cycle with a velocity of $7.2 \text{ km/hr}$ up a hill having a slope of $1$ in $20$. The total mass of the man and the cycle is $100 \text{ kg}$. The power of the man is ............ $\text{W}$. (in $\text{ W}$)

The blades of a windmill sweep out a circle of area $A$.
$(a)$ If the wind flows at a velocity $v$ perpendicular to the circle,what is the mass of the air passing through it in time $t?$
$(b)$ What is the kinetic energy of the air?
$(c)$ Assume that the windmill converts $25\%$ of the wind's energy into electrical energy,and that $A=30\;m^{2}, v=36\;km/h$ and the density of air is $1.2\;kg\;m^{-3}.$ What is the electrical power produced?

The ratio of powers of two motors is $\frac{3 \sqrt{x}}{\sqrt{x}+1}$,which are capable of raising $300 \ kg$ of water in $5 \ minutes$ and $50 \ kg$ of water in $2 \ minutes$ respectively from a well of $100 \ m$ depth. The value of $x$ is:

$A$ body of mass $m$ accelerates uniformly from rest to $v_1$ in time $t_1$. As a function of time $t$,the instantaneous power delivered to the body is