Question

A box weight 1000 N is placed on the ground. The coefficient of friction between the box and the ground is 0.5. When the box is pulled by a 100 N horizontal force, the frictional force developed between the box and the ground at impending motion is
1. 50 N
2. 75 N
3. 100 N
4. 500 N

Answer 1

Correct Answer - Option 3 : 100 N

Concept:

Frictional force resists the motion of the object upon a surface, however, this resisting force is limited, and once the applied force on the body is more than the resisting force the body will start moving.

The value of limiting friction is given by

Limiting friction F = μN

where μ is static friction coefficient between the body and the surface and is the N is the normal reaction of the body to the surface.

Calculation:

Given:

W = 1000 N, μ = 0.5, P = 100 N

Limiting friction force

F = μN

F = 0.5 × 1000 = 500 N

Since the applied force (100 N) is less than limiting friction so the body will be at rest.

 As long as the body is at rest, the friction force between the surface and the body will be equal to the force applied on the body

∴ Friction force = P = 100 N