Which of the following best explains why a car engine must continuously do work even when the car travels at a constant speed on a flat road?

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Question

Which of the following best explains why a car engine must continuously do work even when the car travels at a constant speed on a flat road?

Accepted Answer

B: Work must be done to overcome friction and air resistance forces — At constant speed on a flat road, kinetic energy and gravitational potential energy remain constant. However, friction and air resistance constantly dissipate energy as heat and sound, so the engine must do work to replenish this lost energy. Option D contradicts Newton's first law — no net force is needed to maintain constant speed.

Answer

D: Moving objects always need a net force to maintain constant speed

Answer

A: The engine must increase the kinetic energy of the car continuously

Answer

C: The engine must increase the gravitational potential energy of the car

Answer

B: Work must be done to overcome friction and air resistance forces

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