Essential University Physics: Volume 1 (4th Edition)

Published by Pearson
ISBN 10: 0-134-98855-8
ISBN 13: 978-0-13498-855-9

Chapter 12 - Exercises and Problems - Page 222: 20


a) 47 meters b) Unstable

Work Step by Step

a) We know that at this point, the value of the force, which equals $\frac{dU}{dx}$, must be 0. Thus, we find: $U=mg(.94x-.01x^2) \\ \frac{dU}{dx}=mg(.94-.02x) \\ 0 = mg(.94-.02x)\\x =\fbox{47 meters}$ b) We take the second derivative to find: $ \frac{d^2U}{dx^2}=-.02$ Since this is less than 0, the equilibrium is unstable.
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