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

• A

  $\mu =\frac{1}{\sqrt{3}}$

• B

  $\mu =0.4$

• C

  $\mu =0.8$

• D

  $\mu =\frac{\sqrt{3}}{2}$