Question

A lift is moving downwards with an acceleration equal to the acceleration due to gravity. A body of mass M kept on the floor of the lift is pulled horizontally, if the coefficient of friction is $\mu$, then the frictional resistance offered by the body is

• A. Mg
• B. $\mu Mg$
• C. $2\mu Mg$
• D. $zero$

Answer 1

The correct option is D $zero$

Writing an equation of motion of the body in a vertical direction.
$N=$ normal force on body acting up due to lift
$Mg=$ force due to gravity acting on a body in a downward direction.
$g=$ Acceleration of body in the downward direction

Applying:
Net force $=Ma$ ; $a=acceleration$
$Mg-N=Mg$
$so,N=0$
since Normal force $\left(N\right)=0$

friction force = $\mu$$N$ $=0$