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

[chelsea526]

Homework Statement

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.

Homework Equations

F = ma
Trigonometry formuals

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??

 

[Doc Al]

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.

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

 

[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.

 

[Doc Al]

Im not sure if I should be trying to use this equation

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

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

I really am stumped that you don't know where along the string the bead is.

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