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Average force on a rocket

  1. Jun 10, 2015 #1
    1. The problem statement, all variables and given/known data
    Rocket engine expends 1150 kg of gas in 1 second, with a velocity of -4.50×10^4 m/s. Calculate the average force exerted on the rocket by the gas during that 1.0 second interval

    2. Relevant equations
    F= m(delat)v / (delta)t

    3. The attempt at a solution
    F= (1150kg)(-45000m/s) / 1 s
    -5.175 x 10^7 N
     
  2. jcsd
  3. Jun 10, 2015 #2

    mfb

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    2016 Award

    Staff: Mentor

    I would use a different sign for deltam, but apart from that it is right.
     
  4. Jun 10, 2015 #3

    rude man

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    Homework Helper
    Gold Member

    Your answer is OK except no - sign. The problem implicitly asks for a magnitude.
    But, you should give a bit more detail on why that formula works, starting with conservation of momentum of the rocket/gas system:
    force x 1 sec. = change per second in momentum of rocket = - change per second in momentum of the gas
    etc.
     
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