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Mechanical energy and momentum conservation

  1. Apr 21, 2014 #1
    Mechanical energy is conserved whenever momentum is conserved. T/F?

    My guess is true:
    If momentum is conserved, no external forces are applied on the system. Hence mechanical energy can't change! (No change in PE, no change in KE).

    BUT: My answer booklet says FALSE! Why?
     
  2. jcsd
  3. Apr 21, 2014 #2
    Momentum is conserved when there's an inelastic collision, but kinetic energy isn't. That's one typical example.
     
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