Question

A man tries to push a box of mass 4 kg with a force of 5 N but the box remains stationary If the coefficient of static friction is 0.45, what is the value of the maximum force of friction?

Answer 1

The static friction is a friction between two objects that are not moving relative to each other.

The static friction must be overcome by an external applied force before the object can move.

The max static fraction (Fμ) is defined as the product of the coefficient of static friction (μ) and the normal force (Fn).

Fμ=μ*Fn

The normal force is defined as the net force normal to the surface, for one body had been put on a surface with out any external tension, it equal to the gravitational force (equally in value and oppositely in direction).

$F_{n}=F_{g}=mg=4*9.8=39.2N$

Thus, the max. force of friction will be

Fμ= $0.45 * 39.2 = 17.64N$

Note that: the object will not  be moved until the applied force more than the max. fraction force as we see in our problem.