A man weighing 60 kg is in a lift that descends with an acceleration of 4 cm`cdot s^(-2)`. What force will the man exert on the floor of the lift?

Explanation

If the lift descends with an acceleration a, and if the reaction force exerted by the lift on the man in the upward direction is R, then
mg - R = ma
`therefore` Force exerted by the man on the lift.s floor,
R = mg - ma [ 4 cm`cdot s^(-2)` ]
= 60(9.8 - 0.04) = 585.6 N
If the lift ascends with the same acceleration, then reaction force on the man is,
R. = mg + ma [ 4 cm`cdot s^(-2) = 0.04 m cdot s^(-2)` ]
= 60(9.8 + 0.04) = 590.4 N
When the acceleration of the lift, while descending, is a = g, then from equation (1) , we get, R = mg - mg = 0, for this zero reaction force, the man feels weightless. So, for a lift falling freely with an acceleration g, the man inside it will feel no weight.