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Power/kinematics problem

  1. Nov 27, 2007 #1
    Ive been trying to figure this out and i keep getting stuck.

    A paratrooper pilot fell 380 m after jumping without his parachute opening. He landed in a snowbank, creating a crater 1.4 m deep, but survived with only minor injuries. Assume the pilot's mass was 76 kg and his terminal velocity was 50 m/s.

    (a) Estimate the work done by the snow in bringing him to the rest.

    (b) Estimate the average force exerted on him by the snow to stop him.

    (c) Estimate the work done on him by the air resistance as he fell.


    For part a i tried setting KE+GPE=W

    so .5*76*50^2+76*9.8*380=W

    I got 378024 J and it was incorrect. I dont know if some of my units are wrong or if my steps for solving part a are wrong.

    Any help regarding parts b and c would be appreciated too.






    3. The attempt at a solution
     
  2. jcsd
  3. Nov 28, 2007 #2

    Shooting Star

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    Homework Helper

    In vacuum, you know what his KE at the point of hitting the ground should be. But it's less. Where's the deficit?

    His KE + PE just before hitting the ground is known. In absence of snow, it should be same at any point. Again, how much is the deficit?

    F_av = ma. If initial and final speeds are known, then a can be found, and thus F_av.
     
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