Question

A block of mass m is resting on the floor of a lift. the coefficient of friction between the block and the floor is $\mu$. When the lift is falling freely, the limiting frictional force between block and surface is

• A. $\mu mg$
• B. $\frac{\mu mg}{2}$
• C. $mg$
• D. zero

Answer 1

Answer: (D)

zero

The limiting frictional force between the block and the surface is

$f_{\mu }=\mu mg$. . . . . .(1)

where, $mg=$normal force

When lift is free falling,

Weight, $W=mg=0N$, So there is no normal reaction between the surface of block and the lift.

From equation (1),

$f_{\mu }=0N$

The correct option is D.