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Old Dec 18th 2017, 11:49 AM   #1
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Pendulum Problem

A simple pendulum has a period of 3 seconds on Earth. If it is taken to Planet X, which has the same mass as Earth but a radius of 0.5 the size of Earth's radius, the new period will be what?

I am using T^2/r^3 = Constant to solve for T(x) but I don't think I'm getting the correct answer.

Any help would be much appreciated!

Thank you
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Old Dec 18th 2017, 01:11 PM   #2
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What "constant" did you use, what answer did you get and what do you believe the correct answer should be?

If a planet has the same mass as the earth but 1/2 the radius, the gravitational force at the surface will be 4 times that on the earth. Since the period of a pendulum is inversely-proportional to the square root of the gravitational force, the period is 1/2 as much.
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Old Dec 18th 2017, 01:50 PM   #3
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Thank you. The only thing I donít understand is your statement about the relationship between the gravitational force and period. I studied this subject in my Physics text and cannot find this relationship. Can you please elaborate?
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Old Dec 18th 2017, 01:56 PM   #4
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Try this link:
<wikipedia : pendulum>

Under "Period of oscillation", it gives an equation for the relationship between the period, the length, and gravity.
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