Question

A block of mass $3kg$ is placed on the floor of coefficient of static friction is $0.4$. The force of $3.5N$ applied on the block. Calculate the force of friction and discuss the motion of the body.

• A. $3.5N$, moves
• B. $3.5N$, remains at rest
• C. $11.76N$, moves
• D. $11.76N$, remains at rest

Answer 1

The correct option is B $3.5N$, remains at rest

block is placed on the horizontal plane, so $mg=N$
also maximum friction force is $\mu .N=0.4\times 3\times 10=12N$.
but friction force acts only if there is a tendency of motion. so friction force will be equal to force applied until it reaches its maximum value. After that limiting friction will act and body will start moving.
So $3.5<12$, hence friction acting is $3.5N$ and body will not move.