- #1
Oerg
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Homework Statement
Ok, I am deriving the change in gravitational potential energy at the surface of the Earth and have met with some difficulties.
Homework Equations
[tex]g=GM/r^2[/tex]
[tex] P.E.=-GMm/r[/tex]
The Attempt at a Solution
[tex] \delta P.E. = -GMm/r_f+GMm/r_i[/tex]
Where [tex] r_f > r_i[/tex]
Since
gravitational field strength is approaximately a constant for small changes of r,
[tex] \delta P.E. = -mgr_f + mgr_i[/tex]
But this gives me a negative answer! How can my change in gravitational potential energy be negative when I bring my object from a lower position to a higher poistion in the gravitational field. I have probed the mathematics of the above proof, but it all makes sense to me since g is a constant.