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The rocket launch and changing gravity

  1. Mar 6, 2012 #1
    When a rocket is launched, it starts not with velocity zero, but with the rotation velocity which the Earth gives it. Thus if a rocket is launched eastward, it requires a smaller boost (and if westward, a larger one) to achieve orbit. with a latitude of 31.1 degrees, cos(31degrees) 24902/24 = 393.11 ms/s

    To escape velocity on earth = (2G Mearth / r earth) = 11200ms-1
    So the total velocity that needed for the rocket = 11200 - 393.11= 10806.99ms-1

    I am trying to find the total energy that is needed for the rocket of 1000kg to escape velocity

    i used the question
    m = 1000 x 9.8 N

    E= 1/2 m^2
    = 5.84 X 10^10 J

    my question is : as the further you are away from earth, there will be less gravity. So if i use that equation, would that be accurate assume there is no air friction and the mass of the rocket doesnt change due to the loss of fuel
     
  2. jcsd
  3. Mar 6, 2012 #2

    PhysicoRaj

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    That would be close enough! But the problem is that the accuracy falls as u go on neglecting decreasing mass due to consumption of fuel.
     
  4. Mar 6, 2012 #3
    should i use the equation of E= 1/2 m^2 ?
     
  5. Mar 6, 2012 #4

    PhysicoRaj

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    If u r calculating energy, then of course it'll do. note that, E=1/2mv^2=GMm/r
     
  6. Mar 6, 2012 #5
    but doesnt the changing gravity affect the m ?
     
  7. Mar 6, 2012 #6

    PhysicoRaj

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    Yes but if u really want to solve it u will hav to take an average of that.
     
  8. Mar 6, 2012 #7

    PhysicoRaj

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    more than that...changing mass is a prob.
     
  9. Mar 6, 2012 #8
    for example if a rocket is 1000 kg on earth , what would the gravity be when it is at 300m
     
  10. Mar 6, 2012 #9

    PhysicoRaj

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    If u r dealing with mass, it would be 1000Kg itself. if u r dealing about wight, itll bcom
    W=mg
    =1000*g
    g= gravitational acceleration at 300mts
    u manipulate it...
    g=w/m
    =w/1000
    ul hav to know its weight there.
     
  11. Mar 6, 2012 #10
    how do you find the changing gravity ?
     
  12. Mar 6, 2012 #11

    PhysicoRaj

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  13. Mar 6, 2012 #12

    PhysicoRaj

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    the gravity dosnt change preferentially at 300mts
    observ: g=9.806 in 0mts
    g=9.803at 1000mts

    ok bye..
     
  14. Mar 6, 2012 #13
    okay thank you very much
     
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