Question

A block of mass $M$ is placed on a rough floor of a lift. The coefficient of friction between the block and the floor is $\mu$. When the lift falls freely, the block is pulled horizontally on the floor. What will be the force of friction?

• A. $\mu Mg$
• B. $\mu Mg/2$
• C. $2\mu Mg$
• D. None of the above

Answer 1

Answer: (D)

None of the above

When lift falls freely the normal reaction on block

$N-mg=mg$

$N=0$

so friction force acts on the block=$\mu N=0$