# Homework Help: Tension problem - bead sliding on a string attached to a pole

1. Oct 5, 2011

### chelsea526

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

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2. Oct 5, 2011

### Staff: Mentor

Take advantage of the fact that you know the length of the string. What does that tell you?

3. Oct 5, 2011

### chelsea526

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.

4. Oct 5, 2011

### 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?