Question

An ox can apply a maximum force of 1000N. It is taking part in a cart race and is able to pull the cart at a constant speed of 30 m/s while making its best effort. Calculate the power developed by the ox
(A) 30 W
(B) 30 kW
(C) 300 kW
(D) 3000 kW

Answer 1

Hint:Given the value of force being acted upon a body which results in the motion of the body with constant speed. Since the speed is constant the acceleration produced in the body will be zero. We need to find the power being developed as a result of application of force.

Complete step by step answer:
Force, F= 1000 N
Velocity, v= 30 m/s
Power is defined as the ratio of work done to the time taken. Its unit is J/s or watt, let us multiply force with velocity and see what product we get.
\[\begin{align}
& =F\times v \\
& =N\times \frac{m}{s} \\
& =\frac{Nm}{s} \\
& =J/s \\
& =W \\
\end{align}\]
Thus, it gives the unit of power. So, let us find out the power,
P=Fv
=30000 W
Converting it into kW since 1kW=1000W
=30 kW
So, the correct option is (B).
Additional Information:
Standard unit used to measure power is the watt (W). One watt is equal to one joule of work done per second. P=Fv, in this equation we calculate the power is the instantaneous power.

Note:We are calculating in this problem not just power but it is instantaneous power, because we had taken the velocity at a given instant and had not taken into account any acceleration. The change in energy is basically power.