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: Balancing two rollers on a hill

  1. Feb 9, 2015 #1
    1. The problem statement, all variables and given/known data
    Two rollers, of masses 2kg and 3kg, are connected over a pulley by a massless string. They rest in equilibrium on two inclined slopes, as shown in the diagram to the left. Friction is negligible. What is the distance X?

    2. Relevant equations
    Fg = mg
    Component of Fg parallel to the slope = mgsin(theta)

    3. The attempt at a solution
    Since they are in equilibrium, the forces on both sides must be equal.
    So I created a separate coordinate system for each side and found the forces acting along the slope.

    On the left side, the force of gravity parallel to the slope is (2kg)(10 m/s^2)(sin(theta)). To find theta, I did arctan(.3/.4) to get 36.87 degrees. So therefore (2kg)(10)(sin(36.87)) = 12 N.

    So the right side force must also be equal to 12 N.
    12 N = (3kg)(10 m/s^2)(sin(theta)).
    So now I found this theta by solving the equation and got 23.58 degrees.

    And finally, to find x, I did sin(23.58) = 0.3/x --> x = 0.75 m.

    But the answer is 0.69 m. What did I do wrong?
  2. jcsd
  3. Feb 9, 2015 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

  4. Feb 9, 2015 #3
    Wow, I don't even know why I thought it was sin for so long.
    Thanks, it should be tan.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted