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A boy stands on a weighing machine inside a lift. When the lift is going down with acceleration $g / 4$, the machine shows a reading 30 kgf. When the lift goes upwards with acceleration $g / 4$, the reading would be
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The correct answer is:
$50 \mathrm{kgf}$
While going down, machine reading is $30 \mathrm{kgf}$.
$\begin{aligned} & \Rightarrow m g-N=m\left(\frac{g}{4}\right) \\ & m g-30 g=\frac{m g}{4} ; 3 \frac{m g}{4}=30 g \\ & m=\frac{30 \times 4}{3}=40 \mathrm{~kg}\end{aligned}$
While going up, the reaction would be
$\begin{aligned} & N^{\prime}-m g=m \frac{g}{4} \\ & N^{\prime}=5 \frac{m g}{4}=\frac{5}{4}(40 \mathrm{~kg}) g \\ \Rightarrow \quad N^{\prime} & =50 \mathrm{kgf} .\end{aligned}$
$\begin{aligned} & \Rightarrow m g-N=m\left(\frac{g}{4}\right) \\ & m g-30 g=\frac{m g}{4} ; 3 \frac{m g}{4}=30 g \\ & m=\frac{30 \times 4}{3}=40 \mathrm{~kg}\end{aligned}$
While going up, the reaction would be
$\begin{aligned} & N^{\prime}-m g=m \frac{g}{4} \\ & N^{\prime}=5 \frac{m g}{4}=\frac{5}{4}(40 \mathrm{~kg}) g \\ \Rightarrow \quad N^{\prime} & =50 \mathrm{kgf} .\end{aligned}$
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