4.42. a)
Free Body Diagrams...
Since all the blocks are moving together, we find that
F = m a
N = (2 kg + 3 kg + 4 kg) a
b)
The force on each block can be found by knowing the mass and acceleration.
c)
With the forces 
and 
as I have defined them in the
free body diagrams, we find that
Therefore P = 14.0 N
Q = 8.00 N