Question

A car accelerates on a horizontal road due to the

• A. the road
• B. the driver of the car
• C. the engine of the car
• D. the earth

Answer 1

The correct option is A

the road

Explanation for correct option

In case of option (A)

1. According to the second law of motion, accelerated motion is always due to an external unbalanced force.
2. To accelerate, the car pushes back on the road and the road automatically pushes the tire forward as per Newton's third law.
3. There are lots of other forces going on internal to the car, the internal forces all add to zero
4. But the force directly responsible for making the car accelerate is the road's friction.
5. .Hence option $a$ is correct.

Explanation for incorrect options,

In case of option (B)

1. The driver of the car applies force to start the car engine.
2. But that force does not move the car in the forward direction.
3. .Hence, option (B) is incorrect.

In case of option (C)

1. The engine only makes the tire rotate.
2. Rotation of the tire does not make the car move forward.
3. Hence, option (C) is incorrect.

In case of option (D)

1. The earth applies normal force in the upward direction which is balanced by the car's weight.
2. Thus there is no unbalanced force to accelerate the car in the forward direction.
3. Hence option (D) is incorrect.

Hence option (A), the road is the correct answer.