Question

In rear-wheel drive cars, the engine rotates the rear wheels and the front wheels rotate only because the car moves. If such a car accelerates on a horizontal road, the friction :

• A. on the rear wheels is in the forward direction.
• B. on the front wheels is in the backward direction.
• C. on the rear wheels has larger magnitude than the friction on the front wheels.
• D. on the car is in the backward direction.

Answer 1

Answer: (A), (B), (C)

The correct options are
A on the rear wheels is in the forward direction.
B on the front wheels is in the backward direction.
C on the rear wheels has larger magnitude than the friction on the front wheels.

In the rear-wheel-drive, the wheel tries to push the ground back thereby getting a frictional force in the forward direction. The car then pushes the front wheel thereby receiving a frictional force in the backward direction initiating the rolling motion of the front wheel.
The static friction force acting on the rear wheels is the force that accelerates the car forward. It is considerably larger as it has to move the whole mass of the car whereas the friction force on the front wheels has to provide only sufficient torque to give the front wheels the correct angular acceleration.