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Easy Kinetic Energy Problem

  1. Sep 1, 2009 #1
    1. The problem statement, all variables and given/known data
    A cheetah whose weight is 419 N runs North at a speed of 112 km/h. What is the cheetah's kineticenergy? Is there a direction? Why or why not?

    I got 2.68 x (10^5)
    Is this wrong?
  2. jcsd
  3. Sep 1, 2009 #2

    Doc Al

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    Staff: Mentor

    What units are you using? How did you calculate it? Show what you did.
  4. Sep 1, 2009 #3


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    Homework Helper

    That does not see correct. If it weighs 419N, what is its mass? Convert 112km/h into m/s
  5. Sep 1, 2009 #4
    i got the mass by dividing (419N)/(9.8m/s^2) because F=ma
    then i plugged it into KE=(1/2)m(v^2)
    V=112km/h (i left it in km/h b/c all the multiple choice answers were in km/h)
  6. Sep 1, 2009 #5
    31.1m/s ??
  7. Sep 1, 2009 #6


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    Homework Helper

    The answers were in km/h? But that's a unit of speed, not energy. Are you sure they weren't in joules (symbol J)?
  8. Sep 2, 2009 #7
    i figured it out!
    so yes, 31.1 m/s
    so KE=(1/2)m(v^2) .... (1/2)(419N / 9.8m/s^2)(31.1 m/s)^2
    20,700 kg m^2/s^2

    and i got the same answer as two other people
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