What Forces Act on Three Blocks on a Frictionless Surface?

[ScullyX51]

Homework Statement

Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface by a horizontal force F_vec. (Intro 1 figure) The magnitude of the tension in the string between blocks B and C is T = 3.00 N. Assume that each block has mass m = 0.400 kg

What is the magnitude F of the force?
What is the tension T:AB in the string between block A and block B?

Homework Equations

F=ma

The Attempt at a Solution

I am unsure of how to approach the first part of the problem. For the second part, since t is the only force acting this the block,
I have: T=ma
I solve for A from the first part of the equation where t is given as follows:
t=ma
3=.400a
a=3/.4
a=7.5 m/s^2

I plugged this into to solve for the other tension as follows:
t=ma
t=.4*7.5
t=3

Mastering physics is saying the tension and the acceleration is wrong. Where did I screw up?

 

[LowlyPion]

What is the order of your blocks?

T <---{A}--{B}--{C}

Generally, whatever your force is, the acceleration will be F/(3*m) and then the intermediate tensions would be whatever force is needed to keep the blocks remaining moving with that acceleration.

In the example above that would be 2/3*F between A:B and 1/3*F between B:C