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Homework Help: Unknown variables.

  1. Dec 6, 2009 #1
    1. The problem statement, all variables and given/known data

    Two chain links are connected together and are suspended by a string. The mass of the top link, link#1 is 8kg, while the mass of the second/bottom link #2 is unknown. If an applied force on the string attached to link #1 of 216N[up], and the links experience an acceleration of 2m/s^2 [up] find the mass of link #2 and the force that link#2 exerts on link1

    2. Relevant equations

    The only thing I know is that the mass is equal to the mass of both of the chains put together, so the mass is greater than 8kg.

    3. The attempt at a solution
    I'm not sure what equations I would have to use
  2. jcsd
  3. Dec 6, 2009 #2
    F=ma=sum of all forces. Force 1 is upwards=216. Force downwards is due to gravity.

    To start, consider a tota mass which is equal to m1 + m2 =M m1=8, m2=?

    2*M=(216-Mg) Can you get m2?
  4. Dec 6, 2009 #3
    if we were to sub all of our knows into the equation 2 x M= (216-mg) we would get

    2 x M= (216 - m x 10)

    but then where would we go from there
  5. Dec 6, 2009 #4
    Well this (M) is the total mass. So subtract m1 and you have the unknown mass. Then if you do a Free body diagram, the force that link 2 exerts on link 1 is easily obtained--it is just the weight of link 2 (note weight is not same as mass)
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