Calculating the Starting Angle of a Pendulum Using Geometry and Trigonometry

[ptdreamer]

A student wishes to figure out the starting angle of the pendulum bob in this experiment. The 50 cm mark is directly below the point of support of the pendulum and the distance from the point of support to the center of the bob is 120 cm. The student measures the diameter of the pendulum bob to be 1.04 cm and the diameter of the post to be 0.709 cm.
What is the starting angle (in radians) of the pendulum when the post is at nominal distance 86.6 cm?


I think the equation I should use is A= sin -1 (delta X corr/L)

... but I am not sure how to go about this.

Please help!

 

[LowlyPion]

Welcome to PF.

Perhaps you could describe what angle it is you are trying to determine a little more clearly. Is the pendulum in motion?

You might be better served to provide a drawing.

 

[ptdreamer]

that is the exact question that the professor gave and i am assuming that the pendulum is in motion.

this is the picture that seemed to relate to this problem.

i hope that you can help!

 

[LowlyPion]

That's just a matter of geometry then isn't it?

And your arcsine of the ratio looks just fine to give you the angle.