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Homework Help: Find final velocity and kinetic energy lost.

  1. Mar 4, 2012 #1
    1. The problem statement, all variables and given/known data

    Mass m1=6kg traveling with velocity 4 m/s collides with mass m2=16kg traveling with velocity 3m/s in the direction shown (m2= is at an angle of 60degress). If the two masses stick together, find the final velocity of the combined masses, and the kinetic energy lost.

    2. Relevant equations

    m1v1+m2v2/m1+m2 , 1/2mv^2

    3. The attempt at a solution

    I tried equating 1/2mv^2= m1v1+m2v2/m1+m2 i tried finding the momentum and equate it with the KE but is no the right set up. I trying to come up witht he right set up but thisis the lonly thing that is poping in my head. I'm trying to find the velocity of the combined masses but they cannot be the sum of the masses v=2m i don't know what i'm doing. Help?
  2. jcsd
  3. Mar 4, 2012 #2


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    Science Advisor
    Homework Helper

    Hi ScienceGeek24! :smile:
    That makes no sense. :redface:

    You can't equate energy and momentum, they're completely different.

    Use conservation of momentum (it always applies in a collision), in the x and y directions. :smile:
  4. Mar 4, 2012 #3
    Got it! using conservation of momentum found my velocity and with that i just simply the KEf to calculate the subratction of KE total minues KEf for my kinetic energy lost. Thanks!
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