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Tension problem - bead sliding on a string attached to a pole

  1. Oct 5, 2011 #1
    1. The problem statement, all variables and given/known data

    A 100 g bead is free to slide along an 80 cm long piece of string ABC. The ends of the string are attached to a vertical pole at A and C, which are 40 cm apart. When the pole is rotated about its axis, AB becomes horizontal.



    2. Relevant equations

    F = ma
    Trigonometry formuals

    3. The attempt at a solution

    I am having trigonometry troubles! I only know one angle (90), and one side length (0.40 m). The bead is somewhere along the 0.80 m string, which is where the unknown angle is formed.

    I thought I could use cos90 = 0.40/hyp, however, my calculator doesn't like this formula.
    How can I find the lengths of the sides, so that I may then find the unknown angle??
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Oct 5, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Take advantage of the fact that you know the length of the string. What does that tell you?
     
  4. Oct 5, 2011 #3
    Im not sure if I should be trying to use this equation

    adj^2 + opp^2 = hyp^2 ?

    I really am stumped that you don't know where along the string the bead is.
     
  5. Oct 5, 2011 #4

    Doc Al

    User Avatar

    Staff: Mentor

    That's Pythagorean theorem. It'll do fine.

    Call one of the unknown sides X. What's the hypotenuse in terms of X?
     
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