At some instant, acceleration of 5 kg is 10 m/s² (see fig.). The acceleration of 10 kg at the instant is

Different forces on the two masses are shown in fig.

From fig. (8 a), we have

$\mathrm{T}=5\times 10=50\mathrm{N}$

From fig. (8 b),

$60-50=10{\mathrm{a}}^{\mathrm{\prime }}\text{or}{\mathrm{a}}^{\mathrm{\prime }}=1\mathrm{m}/{\mathrm{s}}^2$