Input power equals output power divided by efficiency

Steps:

• At constant velocity on horizontal road, engine force balances resistive force F, so net force is zero.
• Output power delivered by engine: P_out = F × v.
• Efficiency η = 25% = 0.25 = P_out / P_in.
• Input power P_in = P_out / 0.25 = Fv / 0.25.

Why C is correct:

• Matches formula P_in = Fv / η, where η = 0.25 defines efficiency as ratio of output to input power.

Why the others are wrong:

• A uses 0.4 instead of 0.25, incorrect efficiency value.
• B gives 0.4 Fv, which is output power scaled wrongly, not input.
• D is zero, ignoring any power requirement.

Final answer: C