In this situation three blocks are initially at rest on a table. (
The red block weighs 4 N
The green block weighs 6 N
The blue block weighs 5 N

A hand then applies a constant force, to the right, on the red block. All three blocks accelerate. Which block has the largest magnitude net force?

1. The red one (5/38) (13%)
2. The green one (8/38) (21%)
3. The blue one (7/38) (18%)
4. Equal for all three (18/38) (47%)

When drawing a free-body diagram the key is to isolate one part of the system and draw all the forces being applied to that one part.