1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Newton's Laws Problem-confused

  1. Sep 30, 2007 #1
    Newton's Laws Problem--confused

    This has been frustrating me:


    The pulley in the figure is essentially weightless and frictionless. Suppose someone holds on to m=10.0 kg and accelerates it upward at 4.905 m/s/s. What will then be the tension in the rope given that M=10.0 kg?


    The sum of the forces on m = Ftension + Fhand - Fgravity = ma
    The sum of the forces on M = Ftension - Fgravity = Ma

    I said Fhand= m * upward acceleration

    I tried solving for 'a' on both equations, then set them equal to eachother to solve for Ftension. This gave me a ridiculous answer, and I'm pretty sure I didn't screw up my math. I must have set it up wrong? Please help!

    Attached Files:

  2. jcsd
  3. Sep 30, 2007 #2
    Acceleration of M will also be 4.9 m/s2. Apply F = Ma to get tension. F = Mg - T.
  4. Sep 30, 2007 #3


    User Avatar
    Homework Helper

    Don't assume what Fhand is... you only know that m accelerates upwards at 4.905m/s^2, therefore the other mass accelerates downwards at 4.905m/s^2

    you should get 2 equations with 2 unknowns (Fhand and tension). solve for the tension. careful about signs and directions... remember one mass accelerates upwards, the other accelerates downwards.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook