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Finding magnitude of the tension of a cord

  1. Dec 14, 2009 #1
    1. The problem statement, all variables and given/known data
    A 20kg block is held in equilibrium by two massless cords, A, B. A is attached to the wall and B is attached to the ceiling. Find the magnitudes of the tensions of the cords.

    Visual: http://i758.photobucket.com/albums/xx228/schuyler2_va/untitled.jpg?t=1260816320

    2. Relevant equations
    [tex]\Sigma[/tex] Forces = m*a

    Normal force = mg(cos [tex]\theta[/tex])

    3. The attempt at a solution
    [tex]\Sigma[/tex] Forces = Tension of A + Tension of B + W + N
    Tensions+Weight = ma

    N = mg(cos [tex]theta[/tex])
    W = 0
    Tension A =?
    Tension B=?

    ^not sure how to find the magnitudes
  2. jcsd
  3. Dec 14, 2009 #2


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    Science Advisor
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    Gold Member

    There isn't any normal force in this problem, just gravity and tension forces. Why do you say W=0 when it is given that the block has a mass of 20 kG? And since the block is in equilibrium, sum of forces is 0, because a is 0. When you sum forces, look in the x and y directions separately, or else the problem becomes vectorially overwhelming. Note that the upper cord has an x and y component of tension, while the horizontall cord has a horizontal component only.
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