Chapter 6. Change in kinetic energy if only the gravitational force does work (6-17)

Question

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Question

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Review

In \perpher words, \(\textit{the work done by gravity on an object equals the negative of the change in gravitational potential energy of the Earth-object system}\). If an object descends, the gravitational force does positive work on it (the force is downward and the object moves downward) and the gravitational potential energy of the system decreases (its change is negative).

If an object rises, the gravitational force does negative work on it (the force is downward but the object moves upward) and the gravitational potential energy of the system increases (its change is positive). If an object begins and ends its motion at the same height, the gravitational force does zero net work on it and there is zero net change in the system’s gravitational potential energy.

We can now restate the work-energy theorem for the falling barbell. If we substitute \(W_\mathrm{grav}\) from Equation 6-16 into Equation 6-15, we get: