A box of mass $m\, kg$ is placed on the rear side of an open truck accelerating at $4\, m/s^2$. The coefficient of friction between the box and the surface below it is $0.4$. The net acceleration of the box with respect to the truck is zero. The value of $m$ is :- $[g = 10\,m/s^2]$
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(pseudo force)
$\therefore \quad \mu m g=m a \Rightarrow \mu g=a$
this equation is free from mass $\mathrm{m}$
So this is true for all values of $\mathrm{m}$
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