Object being launched into space

  • Thread starter aeromat
  • Start date
  • #1
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Homework Statement


Complete the chart for a 1kg rock and its trip through the earth's gravitational firled. The rock was powerfully launched straight up from the surface of the earth at 1x10^4 m/s.

Note: An object's kinetic energy must be a (+)-value; a negative value is impossible.


Homework Equations


Eg = -GmM/r
Ek = GMm/2r
mEarth = 6*10^24 kg
Re = 6.4*10^6 m

The Attempt at a Solution


Basically, we had to set distance as a variable, and see how the energies (Ek and Eg) would change.
The total energy is constant, and it is found to be -1.25*10^7 J
Ok If I solve for E for instance, 6 times the radius of the earth, I will get -1.04x10^7 J of Eg. However, when I try to solve for Ek:

Ek + Eg = ET
Ek = ET - Eg
Ek = (-) answer, since the Eg was smaller than the overall ET, which was found to be -1.25*10^7.

Is this still valid?
 
Last edited:

Answers and Replies

  • #2
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mEarth = 6*10^4 kg
The mass of the Earth should be ~ 6x1024 kg:shy:
 
  • #3
gneill
Mentor
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2,792
If the total mechanical energy of the rock is -1.25*107 J, a negative value, then the rock is bound by the Earth's gravity and will not escape. That means that there is a maximum distance it can achieve before it returns to Earth. You should find this distance to make sure that you don't go plugging in distances that it cannot achieve: you'll get nonsense results like negative KE's.
 

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