# physics question

posted by anonymous

A 2kg mass is attached to a 5.50m long string. The mass is pulled 30 degrees from its lowest point and then released. What is the initial height of the pendulum above its lowest point?

I think I should be solving for Lcos(theta), where L = 5.50 and theta = 30, but that gives me the wrong answer.

Why? What is the correct procedure, and how might I visualize it in terms of right triangles?

1. bobpursley

what is 5.5(1-cos30) ? Draw the figure, goodness. you have a Lcos(theta) along the vertical, but that is not all the way down.

2. anonymous

Thank you! I drew the figure and see the differences in the length, but still why is it 1 - cos30?

3. bobpursley

ok, goodness. it is 5.5-5.5cos30.

4. anonymous

oh wow, thanks. I see that.

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