Question

A horizontal force just sufficient to move a body of mass $4\text{kg}$ lying on a rough horizontal surface is applied on it. The coefficient of static and kinetic friction between the body and the surface are $0.8$ and $0.6$, respectively. If the force continues to act even after the block has started moving, the acceleration of the block in ${\text{ms}}^{-2}$ is $(g=10{\text{ms}}^{-2})$

• A. $\frac{1}{4}$
• B. $\frac{1}{2}$
• C. $2$
• D. $4$

Answer 1

The correct option is C $2$

The minimum force required to just move a body will be $f_1={\mu }_{s}mg$. After the motion is started, the friction will become kinetic. So the force which is responsible for the increase in velocity of the block is
$F=({\mu }_s-{\mu }_k)mg=(0.8-0.6)\times 4\times 10=8\text{N}$
So $a=\frac{F}{m}=\frac{8}{4}=2{\text{ms}}^{-2}$