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4-1.Newton's Laws of Motion
hard
A balloon of mass $m$ is descending down with an acceleration $\frac{g}{2}$. How much mass should be removed from it so that it starts moving up with same acceleration?
A
$\frac{{2\,m}}{3}$
B
$\frac{{m}}{3}$
C
$3\,m$
D
$\frac{4}{3}\,m$
Solution
$\Rightarrow m g-F=\frac{m g}{2}$
$F=\frac{m g}{2}$ $…(1)$
$\mathrm{F}-\left(\mathrm{m}-\mathrm{m}_{1}\right) \mathrm{g}=\left(\mathrm{m}-\mathrm{m}_{1}\right) \mathrm{g} / 2$
$\mathrm{F}=\frac{3}{2}\left(\mathrm{m}-\mathrm{m}_{1}\right) \mathrm{g}$ $…(2)$
By equation $( 1 )$ and $( 2 )$
$\begin{aligned} \frac{m g}{2} &=\frac{3}{2}\left(m-m_{1}\right) g \\ m &=3 m-3 m_{1} \\ 3 m_{1} &=2 m \\ m_{1} &=\frac{2 m}{3} \end{aligned}$
Standard 11
Physics