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Escape Velocity Problem

  1. Jan 20, 2013 #1
    1. The problem statement, all variables and given/known data
    A meteoroid with a velocity (when the effect of the Earth's gravity has been eliminiated) of 49.9 km/s when it is at a distance of 1.50x10^11m from the sun.

    (a) Using energy calculations show that this object has an open orbit and is therefore not restricted to our solar system
    (b) Calculate what the velocity of this meteoroid would be when it was infinitely far away from the sun

    2. Relevant equations

    v = sqrt (2GM/r)

    3. The attempt at a solution

    For (a) I just plugged in v = 49 900 m/s
    G = constant
    r = 1.50x10^11m

    And I solved for M which was 9.33x10^30 kg which doesn't equal the earth of the mass so that shows that it isn't part of our solar system.

    Then for (b) I used the same equation I used above and plugged in r = infinity which eventually leads to 0. So does the v eventually go to v = 0 m/s?
  2. jcsd
  3. Jan 20, 2013 #2


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    The first part of the problem says to use energy calculations. So, find the meteroid's energy, and compare it to how much energy is needed to escape the Sun. Don't forget to include kinetic and potential energy.
  4. Jan 21, 2013 #3
    I used the energy formula E = KE + U
    = 1/2mv^2 - GmM/r
    E = 1/2v^2 - GM/r

    Then I plugged in my knowns
    v = 49900 m/s
    G = 6.67x10^-11
    M = 5.98x10^24 kg
    r = 1.50x10^11m

    So the energy of the meteroid in the earth's circuit should be 1.25x10^9 J

    So for the comparison do I compare it to the escape velocity? Because it doesn't workout because E = 0. A little confused.
    Last edited: Jan 21, 2013
  5. Jan 21, 2013 #4


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    You have the formula for escape velocity:

    ve = sqrt(2 G M / r)

    and the velocity of the meteoroid is given:

    vm = 49 kph

    so what do you think the next step should be to determine if the meteroid has achieved escape velocity?

    For the last part of the problem, you could also use the formula for gravitation potential or gravitational potential energy versus distance from the sun.
  6. Jan 21, 2013 #5
    Do I get the escape velocity and compare it to the velocity of the meteoroid?
  7. Jan 21, 2013 #6


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    What would the energy of an object at that location at escape velocity be?
  8. Jan 21, 2013 #7


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    Homework Helper

  9. Jan 21, 2013 #8
    Thank you.
  10. Jan 21, 2013 #9


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    Except that the problem says to use energy calculations.
  11. Jan 21, 2013 #10


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    So that would change this to

    1/2 m ve2 = G M m / r = - GPE of meteroid

    1/2 m vm2 = 1/2 m (49900)2 = KE of meteroid
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