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Homework Help: Newton's LAws and tension

  1. Dec 7, 2008 #1
    1. The problem statement, all variables and given/known data

    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]

    2. Relevant equations


    3. 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=32 * 6.68=187 N
    and that's as far as I got
  2. jcsd
  3. Dec 7, 2008 #2


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    Staff Emeritus
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    Gold Member

    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.
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