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Homework Help: Work and kinetic energy

  1. Feb 26, 2008 #1
    A helicopter is used to lift a 72.7 kg astronaut 16.9 m vertically out of the ocean by means of a cable. The astronaut rises with constant upward acceleration of magnitude 7.23 m/s2 until she reaches the helicopter.

    a) How much work is done by the helicopter on the astronaut?


    W=1/2MV^2=FS


    first try: V^2=2as W=mas=8882.9949J wrong
    second try: F=mg W=mgh=12052.8603J wrong

    someone help me please, thank you so much!!
     
  2. jcsd
  3. Feb 26, 2008 #2
    First find the force required to lift the person. Then use work is force times displacement to find the work.
     
  4. Feb 26, 2008 #3
    is the force mg ?
     
  5. Feb 26, 2008 #4
    Use Newton's Second Law.

    F = m*a

    Force of helicopter - mass of astronaut * g = mass of astro * 7.23

    Therefore the Force the helicopter must exert is 7.23 m + mg

    Work = Force x Distance, so its just (7.23 m + mg) (16.9) Joules. Good luck!
     
  6. Feb 26, 2008 #5
    yeah, i forgot to add the force of helicopter. thank you man!!
     
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