A man in a crate which hangs alongside a building. When the man of mass 50 kg pulls the rope, the force exerted by him on the floor of crate is 250 N. If crate weight is 25 kg. Then

N =250 N . 

Equation of motion of man:

$\mathrm{N}+\mathrm{T}-\mathrm{Mg}=\mathrm{Ma} ········· \left(1\right)$

For crate:

$\mathrm{T}-\mathrm{N}-\mathrm{mg}=\mathrm{ma} ········\left(2\right)$

Adding Eqs. (1) and (2), we get
$2\mathrm{T} -\left(\mathrm{M}+ \mathrm{m}\right) \mathrm{g} = \left(\mathrm{M} + \mathrm{m}\right)\mathrm{a}$

$\Rightarrow 2\mathrm{T} = \left(\mathrm{M} + \mathrm{m}\right)\left(\mathrm{g} + \mathrm{a}\right)$

$\Rightarrow \mathrm{T} = \frac{1}{2}\left[50 + 25\right]\left[10 + 10\right] = 750\mathrm{N}$

Subtracting Eq. (2) from (1), we get

$$\begin{gathered} 2\mathrm{N} -\left(\mathrm{M}+ \mathrm{m}\right) \mathrm{g} =\left(\mathrm{M} + \mathrm{m}\right)\mathrm{a} \\ \Rightarrow 500 - 25 \mathrm{x}10 = 25\mathrm{a}\Rightarrow 250\ne 25\mathrm{a} \\ \Rightarrow \mathrm{a} =10 \mathrm{m}/{\mathrm{s}}^2 \end{gathered}$$