$A$ force $\vec{F} = (4 \hat{i} + \hat{j} - 2 \hat{k}) \text{ N}$ acting on a body maintains its velocity at $\vec{v} = (2 \hat{i} + 2 \hat{j} + 3 \hat{k}) \text{ m s}^{-1}$. The power exerted is $..... \text{ W}$.

$A$ body is moving along a straight line under the influence of a constant power source. If the relation between the displacement $(s)$ of the body and time $(t)$ is $s \propto t^x$, then $x=$

An electric motor produces a tension of $9000 \ N$ on a reel containing an electric cable at a rate of $2 \ ms^{-1}$. Calculate the power of the electric motor in $kW$.

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?

$A$ weightlifter lifts a weight of $300\; kg$ to a height of $2\; m$ from the ground in $3\; s$. The average power generated by him is.....$W$.

Water is falling on the blades of a turbine from a height of $25 \ m$. $3 \times 10^3 \ kg$ of water pours on the blade per minute. If the whole of energy is transferred to the turbine,the power delivered is: (in $W$)