A man of mass 70 kg stands on a weighing machine in a lift , which is moving (a) upwards with a unifrom speed of `10ms^(-1)` (b) downwards with a unifrom acceleration of `5 ms^(-2)`
(c) upwards with a unifrom acceleration of `5 ms^(-2)` What would be th readings on the scale in each case ?
(d) What would be the reading if the lift machanism failed and it hurtled down freely under gravity ?

Explanation

The reading on the scale is a measure of the force on the floor by the man. By the Third Law, this is equal and opposite to the normal force N on the man by the floor.
(a) `N = 70 xx 10 = 700 N : ` Reading is 70 kg
(b) `70 xx 10 - N = 70 xx 5` : Reading is 35 kg
(c ) `N -70 xx 10 =70 xx 5` : Reading is 105 kg
(d) `70 xx 10 -N = 70 xx 10` : Reading would be zero, the scale would be read zero .