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It is easy to calculate your change in gravitational potential
energy in an elevator. Suppose you have a mass 
and the elevator takes you up to a height 
above the ground level. The force 
that would need to raise you is equal to your weight, i.e., 
.
The work done by this force is
The work done is equal to the energy transferred, which is just your gain in potential energy. Thus the expression for the gravitational potential energy of an object is given by
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| Fig. 3-1 The Ocean Park Tower |
Example
A boy of 40 kg is raised to the top of the Ocean Park Tower. If the height of the tower is 72 m, what is his change in potential energy?
Solution
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| Fig. 3-2 Escalator in the Ocean Park |
Example
A section of the escalator in the Ocean Park has a length
of 63.5 m (Fig. 3-2). The track makes an angle of 30
with the horizontal. What is the gain in potential energy of a person
of mass 50 kg in taking the escalator?
Solution
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