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Homework Help: Kinetic energy and momentum of two objects

  1. Jul 12, 2004 #1
    do 2 objects that have the same kinetic energy necessarily have the same momentum? I cant think of a simple example :yuck:
  2. jcsd
  3. Jul 12, 2004 #2


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    Consider a 5 kg mass going at 50 m/s, thus having 6.25 kJ of kinetic energy. Now, a mass of 125 kg going 10 m/s also has 6.25 kJ of kinetic energy. However, the first object has a momentum of 250 kg*m/s, and the second has 1250 kg*m/s of momentum.
  4. Jul 12, 2004 #3
    thanks so much =o) !!
  5. Jul 13, 2004 #4
    what if they both have 0 momentum, so does it follow that the kinetic energy of the system doesnt have to be zero as well? or does it?
  6. Jul 13, 2004 #5

    Doc Al

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    Think about it. For a simple object:
    [tex] KE = 1/2 mv^2[/tex]
    [tex] momentum = mv[/tex]
    The only way an object can have zero momentum is if its speed (v) is what? Then what is its KE?
  7. Jul 13, 2004 #6
    thanks again, i think i just spaced out on that one ;oP
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