Question

A block of mass $m$ is kept on an inclined plane of a lift moving down with acceleration of $2{\text{m/s}}^2$. What should be the coefficient of friction for the block to move down with constant velocity relative to lift?

• A. $\mu =\frac{1}{\sqrt{3}}$
• B. $\mu =0.4$
• C. $\mu =0.8$
• D. $\mu =0.5$

Answer 1

The correct option is A $\mu =\frac{1}{\sqrt{3}}$

Effective acceleration due to gravity is
$g_{eff}=g-2=8{\text{m/s}}^2$
Along inclined plane [for constant velocity w.r.t lift]
$\Rightarrow m(g-a)\text{sin}\theta =\mu m(g-a)\text{cos}\theta$
$\Rightarrow \mu =\text{tan}\theta =\text{tan}{30}^{\circ }=\frac{1}{\sqrt{3}}$