Force Exerted by Blocks on a Frictionless Surface

[farrah003]

1. Homework Statement

Blocks of mass 5, 10, and 25 kg are lined up from left to right in that order on a frictionless surface so each block is touching the next one. A rightward-pointing force of magnitude 14 N is applied to the left-most block.

a) What is the magnitude of the force that the middle block exerts on the rightmost one?
Fright, middle = 8.749999995
b) What is the magnitude of the force that the leftmost block exerts on the middle one?
Fmiddle, left = ?
c) Suppose now that the left-right order of the blocks is reversed. Now find the magnitude of the force that the leftmost block exerts on the middle one?
F'middle, left = ?


i figured out the first part i just need help to do the last two

 

[MHrtz]

I don't think (a) is right. Here's what I would do.

F = ma

The force pushing on the blocks is equal to their total mass times their acceleration but we have to solve for acceleration.

14 = 30a

a = 7/15

Use F = ma for every question and don't forget Newton's 3rd law

 

[farrah003]

part a is correct because the homework is on a software and it accepted my answer

 

[MHrtz]

how did you get a

 

[MHrtz]

Nevermind. I screwed up. The total mass of the blocks is equal to 40 not 30. So a is right.