Question

A block of mass $4kg$ is placed on a rough horizontal plane. A time dependent force $F=k{t}^2$ acts on the block. where $k=2N/s^2$. Coefficient of friction $\mu =0.8$ . Force of friction between block and the plane at $t=2s$ is

• A. $8N$
• B. $4N$
• C. $2N$
• D. $32N$

Answer 1

The correct option is A $8N$

$f_{max}=\mu mg=0.8\times 4\times 10=32N$
At $t=2s,F=k{t}^2=\left(2\right)(2{)}^2=8N$
Since applied force $F<f_{max}$, force of friction will be the applied force itself which is $8N$