Question

A man is standing on a weighing machine placed in a lift. When stationary his weight is recorded as 40 kg. If the lift is accelerated upwards with an acceleration of $2{\text{m/s}}^2$, then the weight recorded in the machine will be $(g=10\text{m/s}{)}^2$

• A. 32 kg
• B. 40 kg
• C. 42 kg
• D. 48 kg

Answer 1

The correct option is D 48 kg

When man is stationary
his FBD
$\Rightarrow N=mg$
$\Rightarrow m=\frac{N}{g}=40\text{kg}$
When lift accelerates, Pseudo force acts as lift is non-inertial frame.
FBD in non-inertial frame

$\Rightarrow N^{{}^{\prime }}=m(g+a)$
$N^{{}^{\prime }}=40(g+a)$
Mass reading $\frac{N^{{}^{\prime }}}{g}=\frac{40(g+a)}{g}=40\left(\frac{12}{10}\right)=48\text{kg}$