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Homework Help: Conservation of Energy (answer in Netwons)

  1. Jan 26, 2012 #1
    Pam has a mass of 47.1 kg and she is at rest on
    smooth, level, frictionless ice. Pam straps on
    a rocket pack. The rocket supplies a constant
    force for 15.3 m and Pam acquires a speed of
    59.2 m/s.
    What is the magnitude of the force?
    Answer in units of N
    The acceleration of gravity is 9.8 m/s^2

    I know the KE= 1/2 mv^2 and that PE=mgh.
    I do not know how to get an answer in newtons however..
     
  2. jcsd
  3. Jan 26, 2012 #2

    mukundpa

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    Do you know work energy theorem?
     
  4. Jan 26, 2012 #3

    Nugatory

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    Staff: Mentor

    You also need the equation for work done by a force acting over a distance.
     
  5. Jan 26, 2012 #4
    I do not! could you please explain?
     
  6. Jan 26, 2012 #5

    mukundpa

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    The theorem says in absence of any Resistance force increase in total energy of a body is equal to the work done on it. Here work is done by rocket pack force.
     
  7. Jan 26, 2012 #6
    and work= power/time right? so how do i solve this if i don't know how long she was moving?
     
  8. Jan 26, 2012 #7

    mukundpa

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    Power is not involved at all.
    work = force*displacement
     
  9. Jan 26, 2012 #8
    oh sorry. well i'm pretty lost then... can you help me any more than this?
     
  10. Jan 26, 2012 #9

    mukundpa

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    work done = gain in PE + gain in KE
     
    Last edited: Jan 26, 2012
  11. Jan 26, 2012 #10
    I surrender.
     
  12. Jan 26, 2012 #11

    mukundpa

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    F*h = mgh + 1/2 mv^2 if it is going vertically
    F*x = 1/2 mv^2 if it is moving horizontally
     
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