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Homework Help: Work done on the jet by the catapult

  1. Feb 23, 2008 #1
    1. The problem statement, all variables and given/known data

    A fighter jet is launched from an aircraft carrier with the aid of its own engines and a steam-powered catapult. The thrust of its engines is 3.14 x 10^5 N. In being launched from rest it moves through a distance of 85.1 m and has a kinetic energy of 5.63 x 10^7 J at lift-off. What is the work done on the jet by the catapult?

    2. Relevant equations


    3. The attempt at a solution

    I am unsure how to start this. They dont give me the final velocity or the mass. so I dont think i can use that equation. Is this a tricky question? Is the answer 5.63 x 10^7 J or 5.63 x 10^7 J times 85.1m= 4.79 x 10^9
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 23, 2008 #2
    You can calculate the word done by the engines with:
    W = Fd

    Then subtract it from the final kinetic energy, the remainder will be the work done by the catapult.
  4. Feb 23, 2008 #3
    so, considering there's no atrit and no potencial energy variation and that fuel is massless , have 2 vital information:
    total work=delta Energy(in case Potencial energy=constant, total work=delta kinectic Energy).

    So, you have
    Energy in the begin and Energy in the end

    and than you know that total work=W1+W2 (where W1 is work of jets and W2 work of catapult)

    I guess you have all...(i don't make the calculations as i prefer letters ratter than numbers...)
  5. Feb 23, 2008 #4
    ok that makes sense now. thank you
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