A vehicle needs an engine of 7500 watt to keep it moving with a constant velocity of 20 m/sec on a horizontal surface. The force resisting the motion is :

Since the vehicle moves with constant velocity, its engine power is consumed completely to overcome forces resisting the vehicle's motion.

Hence, $\mathrm{Fv}=\mathrm{P} \Rightarrow \mathrm{F}=\frac{\mathrm{P}}{\mathrm{v}}=\frac{7500}{20}=375 \mathrm{N}$.