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: Tensional force help

  1. Mar 7, 2006 #1
    A ball hangs from a string on the rear view mirror of a car. The car is accelerating, causing the string to be at an angle theta with the vertical. If the car is accelerating at 1.0m/s2 and the mass of the ball is 4kg, what is the magnitude of the tension on the string, and at what angle is it?

    Fx) -T* Sin (theta) = MA
    Fy) T*Cos(theta) -w=0

    MA= 4 * 9.8 = 39.2
    W= 39.2 + (4 * 1.0)= 43.2
    Fx) -T * Sin (theta)= 39.2

    Fy) T * Cos (Theta) -43.2 = 0
    Fy) T * Cos (Theta) = 43.2

    Could somone point me in the right direction for the next step in finding T? I'm not very strong in math and I'm not sure were to go from here.
  2. jcsd
  3. Mar 7, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    At this point, you're doing fine. I'm not sure what you were doing after that.

    Rewrite your equations like this:
    [tex]T \sin\theta = m a[/tex]
    [tex]T \cos\theta = w = mg[/tex]

    To solve these two equations, try dividing one by the other. See what happens.
  4. Mar 7, 2006 #3


    User Avatar
    Homework Helper

    acceleration a = 1.0 m/s/s ...
    This "a" has ALMOST NOTHING to do with "g" = 9.8 N/kg !

    the weight = Force by gravity = mg , = T cos(theta) .
    T sin(theta) = m a .

    Try drawing a triangle of these components, and see what tan(theta) is ...
  5. Mar 8, 2006 #4
    Thanks! Thats what I needed.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook