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Homework Help: Rocket Thrust Force

  1. Nov 12, 2007 #1
    A toy rocket, of mass 90g, acheives a velocity of 80m/s after 3.0s when fired straight up. What average thrust force does the rocket engine exert?

    I dont' know what formula to use for this
  2. jcsd
  3. Nov 12, 2007 #2


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    Can you find the average acceleration?
  4. Nov 12, 2007 #3
    is this held in earth where gravity exists? lol, i know its a dumb question, but sometimes during my life, i have done problems like these without the involvement of gravity.
    Last edited: Nov 12, 2007
  5. Nov 13, 2007 #4
    avg acceleration = 26.667m/s and lol yea its on earth
  6. Nov 13, 2007 #5
    no help?
  7. Nov 13, 2007 #6


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    Acceleration is in m/s^2.

    So what's Newton's second law?
  8. Nov 13, 2007 #7
    what i did is...

    Fnet = (m*v)/t

    Fnet = (.09*80)/3 = 2.4N

    What did i do wrong?
  9. Nov 13, 2007 #8
    Am i not supposed to be solving for Fnet?
  10. Nov 13, 2007 #9
    Can some1 help i ahve to have this finished by tomorrow and i'm doing it wrong
  11. Nov 13, 2007 #10
    Does it give you a rate at which the mass of the rocket is changing?
  12. Nov 13, 2007 #11
    I think i'm neglecting that.
  13. Nov 13, 2007 #12
    ok, start out by drawing a free-body diagram. since the thrust is accelerating upwards.. thrust must me greater than weight. therefore Ft-W=Ma soo Ft=w+ma, right?

    Solve for a, and then just plug and chug..
  14. Nov 14, 2007 #13
    sweet thanks, i get it now
  15. Nov 18, 2011 #14
    hey, i have the same question, but what does w stand for? since m = mass, Ft = force of thrust anf a = acceleration (right)? then what is w?
  16. Nov 18, 2011 #15


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    What force must the rocket thrust counteract in order for the rocket to rise?
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