Answer
a) $0.1786kg$
b) $0.8624m/s^{2}$
Work Step by Step
a). $T_{1}+coefficient\times m_{3}g=T_{2}$ from previous problem
$m_{3}=\frac{m_{2}g-m_{1}g}{coefficient\times g}=\frac{m_{2}-m_{1}}{coefficient}=\frac{0.25-0.15}{0.56}=0.1786kg$
b). $T_{1}=m_{1}g+m_{1}a$
$T_{2}=m_{2}g-m_{2}a$
$T_{2}-T_{1}-f=m_{3}a$
So, $(m_{2}g-m_{2}a)-(m_{1}g+m_{1}a)-(coefficient\times m_{3}g)=m_{3}a$
a=$\frac{m_{2}-m_{1}-coefficient\times m_{3}}{m_{1}+m_{2}+m_{3}}g=0.8624m/s^{2}$
