Ncert Exercises & Solutions

A person of mass

50

$50$ kg stands on a weighing scale on a lift. If the lift is descending with a downward acceleration of

9 {ms}^{- 2}

$9~\text{ms}^{-2}$ , what would be the reading of the weighing scale?
(Take

g = 10 {ms}^{- 2}

$g=10~\text{ms}^{-2}$ )
1.

50 kg

$50~\text{kg}$
2.

5 kg

$5~\text{kg}$
3.

10 kg

$10~\text{kg}$
4.

100 kg

$100~\text{kg}$

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}

${ms}^{- 2}$
Acceleration due to gravity g = 10

{ms}^{- 2}

${ms}^{- 2}$
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}

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

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