1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    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!

Three masses on a pulley

  1. Oct 26, 2008 #1
    1. The problem statement, all variables and given/known data
    The pulley is massless and frictionless. A massless inextensible string is attached to these masses: 1kg, 3 kg, and 8kg. The acceleration of gravity is 9.8m/s^2. What is the tension T1 in the string between the block with mass 1kg and the block with mass 3kg (on the left hand side of the pulley)?

    Picture of the problem:

    My freebody diagrams for the problem

    Fnet (1kg)= T1- Fg= ma
    T1= Fg +ma

    Fnet (3kg)= T2- T1- Fg= ma

    Other than assuming that T1, T2 and T3 are all the same, I don't really know where to go from there...I would really appreciate it if someone could point me in the right direction.
  2. jcsd
  3. Oct 26, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Your FBD's and application of Newton 2 are good thus far. As a hint, you should note that the tension in a string wrapped around a massless, frictionless pulley is the same on each side of the pulley , but don't assume that all tensions are the same! Now draw a FBD of the 8Kg block, which you have neglected to do. Then where do you go from there?
  4. Oct 28, 2008 #3
    Oh, I see. So T2 and T3 are the same. That helps a lot. Thanks!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Three masses on a pulley