Question

Kinetic friction is directly proportional to:
A) Applied force.
B) Velocity of the body along the surface.
C) Normal reaction.
D) Weight of the body.

Answer 1

Hint: Friction force is the resistance force which stops the motion of anybody. The friction force always acts in the opposite direction of the motion of the body and it depends upon the normal reaction and the coefficient of friction between the body and the surface of ground.

Complete step by step solution:
It is asked in the problem of which option the kinetic friction is proportional to, we need to select the correct option. Kinetic friction is defined as the friction force which acts on a moving body and it acts opposite to the direction of motion of anybody.
The formula of kinetic friction is given by,
$ \Rightarrow {f_k} = {\mu _k} \times N$
Where the frictional force is ${f_k}$, the coefficient of friction is ${\mu _k}$ and the normal reaction is N.
Here the normal reaction of the body is equal to the weight of the body. so the kinetic friction is directly proportional to the normal reaction of the body.

The correct answer for this problem is option C.

Additional information:
There are two types of friction one is the friction which acts on the body when the body is in motion and known as kinetic friction and the other is the friction force which acts when the body is at rest. The coefficient of static friction is more than the coefficient of kinetic friction.

Note: The students are advised to understand and remember the formula of the friction force and specific formula of the static and kinetic friction. The only difference between the kinetic and static friction is the coefficient of friction, in static friction there is static coefficient of friction and in kinetic friction there is static coefficient of friction.