3.a)
A, B, and C are all accelerating with the same acceleration due to the tension in each string. In other words the tension in string P acts on system A in the opposite direction as the tension in string Q, and so on.
b)
**fig**
c)
**fig**
d)
The magitude of the net force on systems B and C are equal and twice the magnitude of the net force on system A.
e)
