Calculating Contact Forces Between Blocks on a Frictionless Surface

[Lannie]

This problem seemed very straightforward but I've somehow missed something...

Three blocks (M1, M2, M3) are in contact with each other on a frictionless, horizontal surface. A horizontal force is applied to M1.

If M1= 1.67kg, M2= 2.67kg, M3= 3.78kg, and F= 16.1 N:

a) what is the magnitude of the contact force between blocks 1 and 2
b) what is the magnitude of the contact force between blocks 2 and 3


I used the formula P=(M2/M1+M2) x F to find these contact forces, but the answers I got were not correct.

for a) I calculated P= (2.67/1.67+2.67) x 16.1
and for b) I calculated P= (3.78/2.67+3.78) x 16.1

This seemed like it should lead to the right answer, but it didn't work. Anyone know what I've done wrong?

 

[Pyrrhus]

Check this thread:

https://www.physicsforums.com/showthread.php?t=44474

 

[Lannie]

that makes sense :) thanks for the help