A man of mass 98 kg, is standing on a weighing machine in a lift. What will be the readings of the weighing machine in the following cases: (i) the lift ascends at 100 cm per second. (ii) The lift descends with an acceleration of 30 cm`cdot s^(-2)` ?
[ g = 980 cm`cdot s^(-2)`]

Explanation

When the lift ascends with uniform velocity ( acceleration a = 0) then , R = mg = 98`xx` 9.8 N.
`= (98 xx 9.8)/(9.8)`kg = 98 kg.
when the lift descends,
R = m(g - a)
98(9.8 - 0.3) [30 cm`cdot s^(-2) = 0.3 m cdot s^(-2)`]
`98 xx 9.5` N
`therefore` Reading of the weighing machine
`= (98 xx 9.5)/( 9.8)` kg = 95 kg