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: Tension problem, check my work?

  1. Mar 18, 2017 #1
    1. The problem statement, all variables and given/known data

    The figure shows two wires that are tied to a 970g mass which revolves in a horizontal circle at a constant 7.5 m/s. What is the tension in the upper wire?

    The wires are both 1m long, and are attached to a pole. The radius is cos(30 degrees). It's an equilateral triangle.

    2. Relevant equations

    ∑F = m*a

    3. The attempt at a solution

    ∑Fy = 0.
    ∑Fx = (m*v^2) / r

    First I looked at the forces in the y-direction. Down = negative.
    The upper rope = T1. The lower rope = T2.

    (.5)T1 - (.5)T2 - mg = 0
    *Solve for T1*
    T2 + 2*m*g = T1 // EQN 1

    Next, in the X-Direction. Inward = positive.

    T1cos(30) + T2cos(30) = (m*v^2)/r
    Plug in value for T1 to solve for T2.
    2*T2*cos(30) + 2*m*g*cos(30) = (m*v^2)/r
    [(m*v^2)/r - 2*m*g*cos(30) ] / (2cos(30) = T2
    T2 = 26.868 N

    Plug into EQN 1 and I got T1 = 46 N
  2. jcsd
  3. Mar 18, 2017 #2


    User Avatar

    Staff: Mentor

    Looks good.
  4. Mar 18, 2017 #3
    Thank you!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted