1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Tension of string on pulley?

  1. Sep 26, 2008 #1
    1. The problem statement, all variables and given/known data

    Suppose the pulley is suspended by a cord C

    Determine the tension in this cord after the masses are released and before one hits the ground. Ignore the mass of the pulley and cords.


    Mass 1 : 1.2kg
    Mass 2 : 3.2kg
    Pulley and String mass is negligible

    2. Relevant equations

    T-m1g = -m1a
    T-m2g = m2a
    Tension of pulley = T(C) -mg - 2T = ma(?)

    3. The attempt at a solution

    So I solved for the tensions in both ropes. Since they're equal I got T=17N
    For acceleraton I got 4.4545455m/s. I'm just not too sure on the equation on the Tension of Cord C. Would it be the equation I mentioned above? When I use that I get an answer around 96. Is that right?
  2. jcsd
  3. Sep 26, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    No, it's much simpler than that. Since the pulley is massless, the sum of the forces on it must add to zero. (Note further that there is no mg term acting on the pulley.)
  4. Sep 26, 2008 #3
    So it's just T(C) = 2T?

    because I was thinking mg was referring to the total weight.
  5. Sep 26, 2008 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Yep, that's all it is.
    You are analyzing the pulley, so mg can only refer to the weight of the pulley, which is zero.
  6. Sep 26, 2008 #5
    Thanks a bunch
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Tension string pulley Date
What is the mass of the book? Sep 27, 2017
Force of rope on a pulley Apr 14, 2017
Calculate Tension in the String Jun 18, 2016