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Gravitational Potential Energy |
When a person
climbs up a ladder, he does work to overcome the downward pull of gravity. This work
corresponds to a change in energy, and this is the gravitational PE.
Although he stays motionless, high on the ladder, W =  PE. That work equals the
product of the force he exerts and the vertical height through which he ascends, h.
Thus, |
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| PE = Fg h |
Given
that the person has a mass m, we can write: |
| PE = mg h = mg (hf-hi) Work results when there is a change in PE in the object. Thus, |
Wnet
= PE = mg (hf-hi)
For simplicity's sake, we limit our activities
to the Earth and assume g is constant. PE, like KE is a relative quantity; even the
idea of "height" is relative. We say that the height at some level is zero
and take the PE with respect to that level, since we're only concerned only with the
changes in PE due to changes in altitude, which then removes the need to deal with the
zero-reference level. This results in the equation: |
| PE = mgh |
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