Pulling Three Blocks Connected By Strings?

|Block A|----|Block B|----|Block C|-----%26gt; F





3 blocks are pulled along a frictionless surface by force F, a horizontal force.





All 3 blocks have the same mass of 0.4 kg and the tension of the string between Blocks B and C is 3 N.





From this, is the tension of the string between A and B 6 N?





How do I find force F? Apparently I first need the acceleration of B then the entire system, so





Is the acceleration of B


F=ma


3=0.4(a)


a=3/0.4


a=7.5?





How do I find the acceleration of the total system after this?





Could someone explain?

Pulling Three Blocks Connected By Strings?
If the force between b and c is 3N, then the force between A and B would be half that , i.e 1.5 N. Force F at Block C would be 3 * 1.5 = 4.5 N.





Acceleration of all 3 blocks is 4.5 = (3*0.4) a





a = 4.5 / 1.2 = 3.75 m/s