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B Thrust over time?

  1. Sep 30, 2016 #1
    This should be a painfully simple question, and yet, I can't find the answer.

    once you have calculated the net acceleration force of an object, how do you figure out how fast it will be going over X seconds?

    example (taken from here: http://sciencelearn.org.nz/Contexts/Rockets/Looking-Closer/Calculating-rocket-acceleration)

    the shuttle rocket has a NET thrust of 5.25 m/s and that thrust is constant for 124 seconds. how do you calculate the speed? (they get 1380 m/s)

    I thought it was 5.25 x (124 ^ 2) = m / s ^ 2 but that answer is way off.
    then i thought, maybe it's linear? 5.25 x 124 ? but that answer wasn't correct either..

    I looked at other pages giving examples, but they all seem to skip the part where they convert the m/s to the final time frame.

    help?
     
  2. jcsd
  3. Sep 30, 2016 #2

    jbriggs444

    User Avatar
    Science Advisor

    The article says 5.25 m/s2 That's not thrust. That's acceleration.

    The article also says: "As the shuttle uses its propellant, it also becomes much lighter, which increases acceleration"

    So the article is clear that the 5.25 is NOT constant for 124 seconds.
     
  4. Sep 30, 2016 #3
    Whoops. I must have glanced over that. how about this (where I originally got stuck on)

    the acceleration of a flashlight in space:

    https://www.reddit.com/r/askscience/comments/dofov/does_a_flashlight_produce_thrust/

    1Kg
    3watt
    =
    10 ^ -8 Newton's of force. for 20 hours (27000 seconds)

    how did he get 2.5 meters every hour after 20 hours of acceleration?

    EDIT:

    of course, now I figure it out:

    ( 3 x 10^ (-8) ) x 27000 = 0.00081 m/s x 60 = 0.0486 m/M x 60 = 2.916 meters per hour. doh >.<

    (I originally forgot that they had their final answer as m/hr not m/sec)

    Thank you for putting up with me!
     
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