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Homework Help: Physics-please check answer

  1. Feb 24, 2014 #1
    Physics--please check answer

    1. The problem statement, all variables and given/known data

    A jet engine applies force of 300 N horizontally to the right against a 50 kg rocket. The force of air friction 200 N. If the rocket is thrust horizontally 2.0 m ,what is the kinetic energy gained by the rocket?

    2. Relevant equations

    I think these equations would be used:



    3. The attempt at a solution

    First I re-arranged the force formula and got a=f/m. Then I substituted (300-100)for f and 50 for m. I simplified it to 2.
    Then I used vf^2=vi^2+2ad and substituted 0 for vi, 2 for a and 2.0 for d. Then I got 2.83 for vf.
    Lastly, I used KE=1/2mv^2 and substituted 50 kg for m and 2.83 for v. My final answer is 200 J. I am not too sure if it is correct. Thanks in advanced!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 24, 2014 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    Looks right.
    You meant (300-200) above, not (300-100) but you did it right anyway.
    There was no need to solve for vf. KE = 1/2 m vf^2 and vf^2 = 8. 8*50/2 = 200.
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