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Homework Help: Newton's Second Law problem

  1. Sep 28, 2009 #1
    1. The problem statement, all variables and given/known data

    A sphere of mass 1.1 × 10^-4 kg is suspended from a cord. A steady horizontal breeze pushes the sphere so that the cord makes a constant angle of 23° with the vertical. Find (a) the magnitude of that push and (b) the tension in the cord.

    2. Relevant equations

    F_g = m*g

    F_net = 0 (since we are in equilibrium)

    3. The attempt at a solution

    I am attempting (b) first, then (a) should follow naturally

    Firstly, since the sphere is not moving, we have

    F_net,y = 0

    So then we can take the sum of the two forces acting along the vertical to get

    F_g,y + T_y = 0

    Where T_y is the vertical component of the tension in the cord. Taking the projection to the y coordinate, and expanding the definition of gravity, we have

    -mg + T*sin(t) = 0


    T = (mg) / sin(t) = (1.1*10^-4)*(9.8) / sin(23) == 27.58 * 10^-4 N

    But this solution isn't working for me.. Any idea where I went wrong?
  2. jcsd
  3. Sep 28, 2009 #2


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    Homework Helper

    T * cos23 = mg.
  4. Sep 28, 2009 #3
    SOH-CAH-TOA, duh...

    Thank you, sir
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