Question

A block of mass $m$ is kept on the floor of a freely falling lift. During the free fall of the lift, the block is pulled horizontally with a force of $F=5\text{N}.$ If coefficient of friction between block and floor is ${\mu }_s=0.1$, then the frictional force on the block will be

• A. $5\text{N}$
• B. $2\text{N}$
• C. $\text{Zero}$
• D. $10\text{N}$

Answer 1

The correct option is C $\text{Zero}$

For freely falling body, acceleration is $a=g$ in downward direction.


Therefore, from FBD of block
$mg-N=ma$
$mg-N=mg$
$\Rightarrow N=0$
As $N=0,$
frictional force $=\mu N=0.1\times 0=0$
(c) option is correct.