Question

A block of mass 4 kg is placed on a horizontal surface. The coefficient of static friction is 0.4. If a force of 7N is applied on the block, then find the frictional force.

Answer 1

Correct option is

C

19N

Static friction is a self-adjusting force.

The limiting value of friction up to which the body stays at rest till it starts moving is given by, F

s

=μmg

where μ is the coefficient of static friction.

Below that limit, the frictional force is equal to the force applied.

Here F

s

=0.8×4×10=32N ; g=10m/s

2

Whereas force applied is 19N less than the limiting value of friction.

Hence Frictional force is 19N.