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: Impulse and Momentum Problem

  1. Nov 8, 2008 #1
    1. The problem statement, all variables and given/known data
    A small 120kg rocket is fired vertically, propelled by an engine with a thrust of 6500N. The engine ejects gas at a rate of 4.5kg/s.
    a) Calculate the change in velocity of the gases relative to the engine
    b) after 20 s what will be the rockets accleration.

    2. Relevant equations
    F * delta T = m * delta V

    3. The attempt at a solution
    (6500-1176)(1) = (120-4.5)delta V
    5324= 115.5V
    V= 46 m/s

    I am not sure if I hav the correct force (because I am not sure if I should subtract Ff), correct mass (because I believe that mass is contant in this formula as there isnt delta M)
    Last edited: Nov 9, 2008
  2. jcsd
  3. Nov 9, 2008 #2


    User Avatar
    Homework Helper

    Hi redred7,

    Yes, the mass is changing. The problem states that every second the mass changes by 4.5kg. So in your equation keep the term that has the change in mass.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook