1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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


    User Avatar
    2017 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

    User Avatar
    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted