How Do Newton's Laws Apply to a System of Hanging Masses?

[cartoonorange]

Homework Statement

Three ballot boxes are connected by cords, one of which wraps over a pulley having negligible friction on its axle and negligible mass. The masses are mA = 32.0 kg, mB = 40.0 kg, mC = 18.0 kg. (box a is on the horizontal suface and b and c hang down.

(a) When the assembly is released from rest, what is the tension in the cord that connects boxes B and C?

(b) How far does box A move in the first 0.250 s (assuming it does not reach the pulley)?[/B]

Homework Equations

F=ma

The Attempt at a Solution

First I found acceleration.
T=Mass of box a * acceleration
F gravity = (mass of b + mass of c) * g
T-F gravity = (Mass of b + mass of c) * -accelleration
acceleration=((mass of b + mass of c) *g)/(mass of a +mass of b + mass of c)
a=(58 * 9.8)/(32 + 40 + 18)=6.68
T=ma
T=32 * 6.68=187 N
and that's as far as I got

 

[Hootenanny]

Welcome to Physics Forums,

A hint for part (b): you know the acceleration of box A as well as the initial velocity and the time period.