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

Explanation

Here m = 70 kg , g `= 10 ms^(m/s^(2)`
The weighting machine in each case measueres the reaction R i.e. the apparent weight.
(a) When the lift moves upwards with a uniform speed, its acceleration is zero . R = mg = `70 xx 10 `= 700 N
(b) When the lift moves downwards with a = 5 `ms^(-2)`
R = `m(g - a) = 70( 10 - 5)` = 350 N
(c ) When the lift moves upwards with a = `5ms^(-2)`
R =` m(g + a) = 70 (10 + 5)` = 1050 N
(d) If the lift were to come down freely under gravity , downward acc. a = g
`therefore` R = m(g-a) = m(g-g)` = Zero.