a
\(\begin{array}{l}
Given\,{m_1} = 5kg;{m_2} = 10kg;\mu = 0.15\\
For\,{m_1},\,{m_1}g - T = {m_1}a\\
\Rightarrow 50 - T = 5 \times a\\
and,\,T - 0.15\left( {m + 10} \right)g = \left( {10 + m} \right)a\\
For\,rest\,a = 0\\
or,\,50 = 0.15\left( {m + 10} \right)10\\
\Rightarrow \,5 = \frac{3}{{20}}\left( {m + 10} \right)\\
\frac{{100}}{3} = m + 10\,\,\,\therefore \,m = 23.3\,kg\,;
\end{array}\)
