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Kinetic, potential and mechanical energy question.

  1. Jan 25, 2008 #1
    1. The problem statement, all variables and given/known data
    A 5.5 x 10^4 kg airplane, travelling at an altitude of 9.9 km, has a speed of 260 m/s relative to the ground. Nearing the end of the flight, the plane slows to a speed of 140 m/s while descending to an altitude of 2.1 km. Determine the plane's total loss of mechanical energy during this change of speed and altitude.

    2. Relevant equations
    [tex]E_g = mgh[/tex]
    [tex]E_k = \frac{1}{2}mv^2[/tex]


    3. The attempt at a solution
    I have no idea how to start to solve this problem. If someone could point me in the right direction, it would be great.
     
  2. jcsd
  3. Jan 25, 2008 #2

    Doc Al

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    Staff: Mentor

    The mechanical energy is just the sum of gravitational PE and kinetic energy. You have the formulas for both--just crank it out.
     
  4. Jan 25, 2008 #3
    Thanks dude!
     
  5. Jan 25, 2008 #4
    Ok, I did this:

    a)
    Eg = mgh
    Ek = mv^2, where v I put 260 m/s
    Et1 = Eg + Ek

    b)
    Same thing as above but with the second values.
    Elost = Et1 - Et2.

    The answer is supposed tob e 5.5 x 10^9 Joules but i get 4.98 x 10^9 Joules. What did I do wrong? Did I go about this the right way?
     
  6. Jan 25, 2008 #5

    Doc Al

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    Staff: Mentor

    Looks like the right way to me. If you post the details of your calculation, perhaps we can spot an error. (Or confirm your answer.)
     
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