Side-by-Side Blocks with Force pushing it

ifeelretarded

1. The problem statement, all variables and given/known data
Three blocks are in contact with each other on a frictionless, horizontal surface. A horizontal force F is applied to m₁. If m₁= 2 kg, m₂= 3 kg, m₃= 4 kg, and F= 18 N, find (a) the acceleration of the blocks, (b) the resultant force on each block, and (c) the magnitude of the contact forces between the blocks.


2. Relevant equations
(a) F - N₁₂ = m₁a
N₂₁ - N₂₃ = m₂a
N₃₂ = m₃a

(b) R₁ = m₁a
R₂ = m₂a
R₃ = m₃a

3. The attempt at a solution
(a) I found that a= 2 m/s²

(b) R₁ = 4 N
R₂ = 6 N
R₃ = 8 N

(c) I have no idea what "the magnitude of the contact forces between the blocks" means. Can somebody please tell me if I've done (a) and (b) right? And how to do (c)?

rl.bhat

Hi ifeelretarded, welcome to PF.

Your part a is correct.
To find the contact force, find the net force acting on each block.
The net force acting on m1 is
F - F1 = m1*a, here F1 is the contact force between m1 and m2.
Similarity you can find tha contact force between m2 and m3.

rl.bhat

Hi ifeelretarded, welcome to PF.

Your part a is correct.
To find the contact force, find the net force acting on each block.
The net force acting on m1 is
F - F1 = m1*a, here F1 is the contact force between m1 and m2.
Similarity you can find tha contact force between m2 and m3.

ifeelretarded

So F1 was already previously found in part (b)?

rl.bhat

No. R1 is the net force
R1 = 18N - F1.
Find F1.