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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

    gneill

    User Avatar

    Staff: Mentor

    Looks good.
     
  4. Mar 18, 2017 #3
    Thank you!
     
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