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Homework Help: Systems in equilibrium

  1. Aug 5, 2014 #1
    1. The problem statement, all variables and given/known data
    When a 50-kg mass on a pulley is allowed to drop, the friction in the pulley creates a constant 200 N force upward. What is the tension in the rope?

    2. Relevant equations
    F (upward) = F (downward)

    3. The attempt at a solution
    I attempted this problem by assigning the upward force as 200 N and the downward force as mg, 500 N. My answer was 500 N but the correct answer is 200 N. Conceptually, this makes sense, but I cannot see how this works mathematically. Could someone please explain how equilibrium plays a role in pulley problems like this?
  2. jcsd
  3. Aug 5, 2014 #2


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    Homework Helper

    If the mass is allowed to drop, then why would there be equillibrium? Maybe I'm misunderstanding the set-up?

    Equillibrium is when [itex]\sum F=0[/itex] (and also [itex]\sum \tau =0[/itex])
  4. Aug 5, 2014 #3
    Sorry, the applicable formula would be: F(upward) + ma = F (downward). I was confused with torque.
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