Question

Consider a vehicle going on a horizontal road towards the east. Neglect any force by the air. The frictional forces on the vehicle by the road………
This question has multiple correct options
A. is towards east if the vehicle is accelerating
B. is zero if the vehicle is moving with a uniform velocity
C. must be towards the east
D. must be towards the west

Answer 1

Hint: In order to solve this problem we need to understand that when something is sliding on the frictional surface then the frictional force is opposite to the movement of the body and if it is rolling then the frictional force is towards the movement of the body. In walking also frictional force is in the same direction as the movement of the body. Knowing this will solve your problem and will give you the right answer.

< b>complete step-by-step answer
As we know that the frictional forces always try to oppose the change.
Here it wants to oppose the torque.
The figure of the rolling wheels of the vehicle can be drawn as:

When the vehicle is accelerating then to oppose the rotational torque the friction force should act towards the east. For uniform velocity, the friction is zero.
Hence the frictional force will be towards the east if it is accelerating and is zero if it is moving with uniform velocity.
So, the correct options are A and B.

Note: When you get to solve such problems you need to know that frictional force always tries to oppose the change, that is if the vehicle is accelerating due to torque then it will try to cancel the torque and it will arise itself in the direction opposite to that of torque. Frictional forces oppose the motion when the body is sliding and it is towards the motion when the body is rolling. These forces have advantages and disadvantages as well. It helps when the vehicle turns itself in a turn then frictional force acts as a helper to cancel out the centrifugal force it also helps in the banking of roads. Knowing these things will help you further and will solve your problem.