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Rocket Problem: Determining the amount of fuel burned

  1. Feb 7, 2013 #1
    The set up:
    A 20,000kg rocket has a motor that generates a thrust of 3x10^5 N.


    The problem:
    a)What is it's initial Acceleration?

    b)At an altitude of 5,000m the rockets acceleration has increased to 6 m/s^2, what mass of fuel has it burned?

    Relevant equations:

    F = ma

    The attempt at a solution:

    I found the initial Acceleration to be 5.2 by taking the difference of the thrust and the rockets weight and dividing my the initial mass.

    Part two is the one I cant figure out...I dont think the height of the rocket has anything to do with the solution does it?
     
  2. jcsd
  3. Feb 7, 2013 #2

    haruspex

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    I agree, the altitude is unnecessary. In fact, it's a bit odd because you could calculate the altitude, and I'll bet it's not 5km exactly.
     
  4. Feb 7, 2013 #3
    How do I determine the amount of fuel burned?
     
  5. Feb 7, 2013 #4

    haruspex

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    Recall how you calculated the initial acceleration. Why does the acceleration increase? What, in your calculation, will have remained constant?
     
  6. Feb 7, 2013 #5
    OH...thanks. I get it now. The Thrust is constant the only thing that changes is the mass. Which I can solve for.


    Thank you!
    Ockham
     
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