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Homework Help: Could someone PLEASE quickly check if my work is right?

  1. Oct 6, 2008 #1
    1. The problem statement, all variables and given/known data
    Basically there's a 1.00 kg object hanging in the air attached to a string which is attached to a 0.1487 kg object that is on a table, and they're connected with a pulley.

    the 1.00 kg object pulls the 0.1487 kg a distance of 0.89 m in 1.22 s and then stops when it hits the ground, i need to find the coefficient of friction

    ok so..

    first i found the final velocity of the object
    which is 0.89 m / 1.22 s which gave me a final velocity of 0.7295 m/s

    then i found the acceleration of the entire body by doing

    a = (vf - vi)/t which gave me an acceleration of 0.597957 m/s^2

    The Fnet of the entire body is

    Fnet = [(0.100kg ) + (0.1487kg )] * (0.597957 m/s^2)
    = 0.14871 N
    This is the actual net force with the friction

    so the acceleration of the 0.100 kg falling down without the tension should be just

    mg = (0.100)(9.8)
    = 0.98 N

    so the friction force should be
    0.98 N - 0.14871 N
    = 0.83129 N

    This is the friction force.

    The coefficient of friction is

    Ff = uFn
    so 0.83129 N = u(mg)
    0.83129 N = u(0.1487 kg * 9.8 m/s^2)

    u = 0.5704

    Please i need help URGENT
  2. jcsd
  3. Oct 6, 2008 #2
    Re: [URGENT!!!!!] Could someone PLEASE quickly check if my work is right?

    Well I can tell you that you got the final velocity wrong in your first equation. You completely ignored the fact that the object is accelerating under the force of gravity. What you did was the average velocity perhaps.
    Try this: Vfinal = Vinitial + at
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