Water falls from a dam at a height of $550 \ m$ onto a turbine at a height of $50 \ m$ at a rate of $2000 \ kg$ per second. If the efficiency of the turbine is $80\%$,the power generated is ............. $MW$.

An electric motor produces a tension of $4500 N$ in a wire and the reel winds at a rate of $2 ms^{-1}$. What is the power of the electric motor?

$A$ pump on the ground floor can pump up water to fill a tank of volume $30 \ m^3$ in $15 \ minutes$. If the tank is $40 \ m$ above the ground and the efficiency of the pump is $30\%$,then the electric power consumed by the pump is ....... $kW$.

The average work done by a human heart while it beats once is $0.5 \, J$. Calculate the power used by the heart if it beats $72$ times in a minute.

Water falls down a $500.0 \,m$ shaft to reach a turbine which generates electricity. How many $m^3$ of water must fall per second in order to generate $1.00 \times 10^9 \,W$ of power? (Assume $50 \%$ efficiency of conversion and $g=10 \,ms^{-2}$)

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?