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# I don't understand why the answer in the textbook is a factor of 100 out (M3) watch

1. A girl sets a gyroscope spinning by means of a thread 80cm long. When she has pulled it through x cm, she is exerting a force of (20 + x/4) newtons. Find the kinetic energy of the gyroscope when the whole thread has been pulled through.

Basically I just integrated the function for force with respect to x between the limits of 0 and 80 cm giving 2400J, however the answer in the textbook is 24J. Have I forgotten to do something with the units? Help please.
2. Convert cm to m?

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3. Doesn't give you the answer of 24J, integrating gives 20x + 1/8(x)^2, then using 0.8m as the limits gives 16.08. Not 24.

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Updated: September 13, 2015
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