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!

Question about the upthrust of a rocket

  1. Dec 25, 2016 #1
    1. The problem statement, all variables and given/known data

    The Saturn V rocket which launched the Apollo space missions had the following specifications: mass at lift-off = 3.0 x 10^6 kg velocity of exhaust gases = 1.0 x 10^4 m/s initial rate of fuel consumption at lift-off = 3.0 x 10^3 kg/s 1.(a) Calculate: (i) the force (thrust) produced at lift-off (ii) the resultant force acting on the rocket at lift-off

    2. Relevant equations

    Ft = mv

    3. The attempt at a solution

    i got the force exerted by the exhaust gases by rearranging the equation to F = mv/t. Upthrust was 33MN. But then i have no clue how to figure the second part out, the solution page says it is 3.6MN, i keep getting 3MN, any help would be greatly appreciated!
  2. jcsd
  3. Dec 25, 2016 #2


    User Avatar

    Staff: Mentor

    I don't see how you got the thrust value of 33 MN from the given information, notr how they arrived at 3.6 MN for the resultant force. Check the given value for the exhaust velocity: Was it perhaps a bit higher than 1.0 x 104 m/s?
  4. Dec 25, 2016 #3
    My bad, it's 1.1*10^4 m/s
  5. Dec 25, 2016 #4


    User Avatar

    Staff: Mentor

    Does that resolve your issues?
  6. Dec 25, 2016 #5
    I'm still getting 3MN for the net force, and 33MN for the upthrust
  7. Dec 25, 2016 #6
    It seems like the book used 9.81 as a value for g although it stated to use 10 = g, anyways i've got it :D
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Question about the upthrust of a rocket
  1. Upthrust question (Replies: 3)

  2. A rocket question (Replies: 17)

  3. Rocket Question (Replies: 1)

  4. Question on upthrust (Replies: 4)