At a particular point, a satellite in an elliptical orbit has a gravitational potential energy of 7000 MJ with respect to Earth’s surface and a kinetic energy of 4000 MJ. At another point in its orbit, the satellite’s potential energy is 2000 MJ. What is its kinetic energy at that point? Show all calculations leading to your answer.

Question

At a particular point, a satellite in an elliptical orbit has a gravitational potential energy of 7000 MJ with respect to Earth’s surface and a kinetic energy of 4000 MJ.  At another point in its orbit, the satellite’s potential energy is 2000 MJ.  What is its kinetic energy at that point?  Show all calculations leading to your answer.

theeric · Answer

With the conservation of energy, we know that the total energy is always the same. For this problem, let's assume that there are no other energies that change for the satellite than the potential and kinetic energies.

Then the sume of the energies before has to equal the sum of energies after!

anonymous · Answer

so i got this as my answer but the teacher said someithing about it was wrong  Initially, TME = GPE + KE = 11 000 MJ
so later, when GPE = 2000 MJ, it must be that KE = 9 000 MJ.

theeric · Answer

Huh! That's what I figured would be the answer, too. Did the teacher say $\sf why$ it was wrong?

anonymous · Answer

she didnt say it was all wrong she said something sabout it was wrong but diodnt tell me what

theeric · Answer

That's interesting.. Did she only glance at it?

If that is the whole problem, and your answer included the correct units and the correct number (9,000 MJ, like you said), then I believe that the answer is correct, despite what your teacher said...

anonymous · Answer

ok ill just go with it hah

theeric · Answer

Teachers are human - they make mistakes, too.

theeric · Answer

If she disagrees, then ask her how the conservation of energy should be applied otherwise. :P

New question, then!