$A$ particle is acted upon by a constant power. Then, which of the following physical quantity remains constant?

$A$ $750 \,W$ motor drives a pump which lifts $300 \,L$ of water per minute to a height of $6 \,m$. The efficiency of the motor is nearly (Take,acceleration due to gravity to be $10 \,m/s^2$) (in $\%$)

An electric motor exerts a force of $40\, N$ on a cable and pulls it by a distance of $30\, m$ in one minute. The power supplied by the motor is .............. $W$

An engine pumps water through a hose pipe. Water passes through the pipe and leaves it with a velocity of $2\, m/s$. The mass per unit length of water in the pipe is $100\, kg/m$. What is the power of the engine $?$ ................ $W$

$A$ car of mass $2000 \ kg$ is accelerating from rest. If its engine is supplying a constant power of $10 \ kW$,then the velocity of the car at a time of $10 \ s$ is: (in $m \ s^{-1}$)

An elevator can carry a maximum load of $1800 \; kg$ (elevator $+$ passengers) and is moving up with a constant speed of $2 \; m s^{-1}$. The frictional force opposing the motion is $4000 \; N$. Determine the minimum power delivered by the motor to the elevator in watts as well as in horsepower.