Ncert Exercises & Solutions

A person of mass \(50\) kg stands on a weighing scale on a lift. If the lift is descending with a downward acceleration of \(9~\text{ms}^{-2}\), what would be the reading of the weighing scale?
(Take \(g=10~\text{ms}^{-2}\))
1. \(50~\text{kg}\)
2. \(5~\text{kg}\)
3. \(10~\text{kg}\)
4. \(100~\text{kg}\)

When a lift descends with a downward acceleration a the apparent weight of a body of mass m is given by
w'= R = m(g — a)
Mass of the person m = kg
Descending acæleration a = 9

{ms}^{- 2}

Acceleration due to gravity g = 10

{ms}^{- 2}

The apparent weight of the person,

\begin{array}{l} R = m (g - a) \\ = 50 (10 - 9) \\ = 50 N \\ ∴ Reading of the weighing scale = \frac{R}{g} = \frac{50}{10} = 5 kg . \end{array}

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