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Question about momentum

  1. Nov 1, 2006 #1
    two questions actually:

    1. In a system with two moving objects, when a collision occurs
    between the two objects,
    what is conserved?

    a. the total kinetic energy is always conserved
    b. the total momentum is always conserved
    c. the total kinetic energy and total momentum are always conserved
    d. neither the kinetic energy nor the momentum is conserved
    e. the total momentum is never conserved

    -from what I understand B is the right answer, and If the collision was elastic C would be true, but in this case I think B is the right answer cuz I know in an isolated collision momentum is always conserved.


    with this next question Im having trouble finding the equation I need if anyone can point me in the right direction.

    2. A 50 kg swimmer dives horizontally off a 75 kg rowboat. If the
    speed of the rowboat
    immediately after the swimmer dives off is 1.0 m/s, what speed did
    the diver leave the
    rowboat?
     
  2. jcsd
  3. Nov 1, 2006 #2
    any feedback?

    ive been trying to figure out the 2nd one and I get something like this

    75kg/1 m/s = 75

    now do I just divide? 75/50 kg = 1.5 m/s ?
     
    Last edited: Nov 1, 2006
  4. Nov 1, 2006 #3

    Doc Al

    User Avatar

    Staff: Mentor

    You are correct. (The key word in this question is "always".)

    What's conserved?
     
  5. Nov 1, 2006 #4
    well, the momentum.

    ive been trying to figure out the 2nd one and I get something like this

    75kg/1 m/s = 75

    now do I just divide? 75/50 kg = 1.5 m/s ?
     
  6. Nov 1, 2006 #5

    quasar987

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    Science Advisor
    Homework Helper
    Gold Member

    Yes. Since momentum is conserved, it must be that 75*1 = 50*(speed of the diver).
     
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