Question

A block of mass 4 kg is kept on a rough horizontal
surface. The coefficient of static friction is 0.8. If a force
of 19 N is applied on the block parallel to the floor, then
the force of friction between the block and floor is:
(a) 32 N
(b) 18 N
(c) 19 N
(d) 9.8 N​

Answer 1

Answer:

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, Fs=μmg

where μ is the coefficient of static friction.

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

Here Fs=0.8×4×10=32N ;   g=10m/s2

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

Hence Frictional force is 19N