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Rocket dynamics

  1. Apr 28, 2008 #1
    The weight of a rocket is 80kN at the instant it takes off , and the products of the combusion are ejected at a velocity of 0.60 kms-1 relative to the rocket. Calculate the rate at which the rocket must be consuming fuel in order to take off vertically. Ans: 134kgs-1

    Cant find a solution despite numerous attempt , anyone can help ?
     
  2. jcsd
  3. Apr 28, 2008 #2

    Hootenanny

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    Welcome to PF icymage,

    Could you perhaps detail your attemps to that we can see where your going wrong?
     
  4. Apr 28, 2008 #3
    hmm i tried using the equation f = m(dv/dt) + v (dm/dt) and p = mv and i cant get the answer. Anw this isnt coursework/schoolwork it is a question i stumbled upon on a old textbook of mine.
     
  5. Apr 28, 2008 #4

    Hootenanny

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    Take a look at this excellent Rocket Dynamics Tutorial by D_H, and see if it helps clarify things.
     
  6. Apr 28, 2008 #5

    tiny-tim

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    Welcome to PF!

    Hi icymage! Welcome to PF! :smile:

    This isn't really a caluclus question … it would be if you were asked to find the fuel used to reach a certain time, for example … but you're only asked for the initial fuel used while the speed is zero.

    Hint: how much acceleration does the fuel have to produce before the rocket lifts off?

    how much mass and velocity produce that acceleration? :smile:
     
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