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Anonymous asked on November 12, 2007 Answers (1)

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A student lies on a very rigid board with a scale undereach end. Her feet are directly over one scale.

a) What is the students weight

b) Approximately how far from her feet is the students centerof gravity

I found this where someone posted it but i do not understand how they get part B. Please explain.

The students weight must be the total of the twoscales,    165 pounds

As for the distance from the feet to the center ofmass...   we can consider torques about the cm due to theforces from the two scales. The scale on the right is adistance   "x" from the center of mass, while the scaleon the left is    2 - x   from the cm.Then

     65 * (2 - x) = 100 *x

      130 - 65 x = 100 x

         x =   0.788meters            this is how far the students feet are from his center of mass

How do they get 0.788m?

Explanation / Answer

65 * (2 - x) = 100 *x

130 - 65 x = 100 x

so 130 = 100x + 65x = 165 x

so x = 130 / 165 = 0.7878 = 0.788 (approx)

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