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: Motion in 2 Dimensions - Pulleys

  1. Mar 31, 2008 #1
    1. The problem statement, all variables and given/known data
    Two masses A and B and of mass 1.6kg and 2.4kg respectively are connected be a light string which passes over a a frictionless trolley.
    a) The accelaration of the 1.6kg mass.
    b) The tension in the string
    c) The net force on the 2.4kg mass
    d) The Kinetic Energy of the 1.6kg Mass 0.5s the two masses are released.

    2. Relevant equations
    P=MV - M yes, V no, P no
    u= v+at
    v^2 = U^2 + 2as

    3. The attempt at a solution
    On first glance, it seems there is not enough data to be able to work out Acceleration. Am I right?

    I request that some helpful user will be able to show a way to work the problem out, with the given data, and how Tension can be calculated. Im not asking that someone will do my homework, just that someone will help me work acceleration because I dont think there's enough data

    Thank you in Advance.

    Kindest Regards,
    The Kovac
    Last edited: Mar 31, 2008
  2. jcsd
  3. Mar 31, 2008 #2


    User Avatar
    Homework Helper

    Yes there is sufficient info I believe.

    Start with drawing a free body diagram.

    What are the forces acting on the 1.6kg mass? Similarly, what are the forces on the 2.4kg mass?

    Assume the motion is downward with respect to the 2.4kg mass (meaning the 2.4kg mass moves down). ( Both would accelerate at the same rate so...)

    What is the equation relating the resultant force for the 2.4kg mass?
    What is the equation relating the resultant force for the 1.6kg mass?

    If you did it correctly, you should see a way to get the acceleration and tension.
  4. Apr 1, 2008 #3
    draw free body dig.and use
    net f(on a body)=ma(of that body).
  5. Apr 1, 2008 #4
    IS not the acceleration Zero? The question does not mention any details regarding any movement, so there has to be no acceleration, no?

    If there is acceleration, would not that be 9.8m/s due to gravity? The answer is 1.6m/s but little data a figure such as that I am struggling to find.

    Thank you for the assistance.
  6. Apr 1, 2008 #5
    The acceleration would not be that of gravity, as there are other forces you must take into consideration. Also, there is an acceleration.
  7. Apr 1, 2008 #6
    Also, I would hope the answer for acceleration is not 1.6 m/s; that is velocity.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook