Question

Using a horizontal force of $200N$, we intend to move a wooden cabinet across a floor at a constant velocity. What is the friction force that will be exerted on the cabinet?
A. 20N
B. 200N
C. 0N
D. 220N

Answer 1

Hint: Here, we use the concept of Newton’s third law of motion, which states that to every action, there is an equal and opposite reaction. So that equal magnitude of force applied in the opposite direction.

Complete step by step answer:
We know that, ${\text{F = ma}}$ where m is mass and ( a ) is acceleration.
If a=0 (because we move on a floor at constant velocity)
$\therefore {\text{F = 0}}$ But mass can’t be zero.
According to the question, ${\text{F = 200N}}$, but at constant velocity. There is no acceleration for the cabinet. Thus the net external force becomes zero. In vertical direction its weight cancels out the normal reaction force due to the ground on the cabinet.
In horizontal direction, the frictional force has to cancel the applied force of $200{\text{N}}$, so that no acceleration acts on the body and it moves with constant velocity. Thus the frictional force has the same magnitude as an applied force but exactly opposite in direction. Hence the magnitude of the force is 200N and its direction is opposite to the applied force.

Note: Frictional force means that two surfaces are in contact and slide against each other. This force is mainly affected by the surface texture. The main cause of friction is due to attraction known as adhesion force.