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Homework Help: Conservation of Momentum and Kinetic Energy

  1. Nov 19, 2008 #1
    1. The problem statement, all variables and given/known data

    I was wondering if a glider hits a rubber band bumper is kinetic energy conserved? I can't tell if the data I have supports conservation or loss. I am writing a lab report and data shows that momentum had around a 5% change. Kinetic energy had a 10%-15% change. Momentum is always conserved in a collision so I can conclude its conservered in this case. What is worrying me is that my data is wrong because momentum had a 5% change, I am not sure at what percentage makes it not conserved. I think Kinetic energy is not conserved in this case. Am I right?

    Mass ~ 0.1833

    Velocity Before

    Velocity After
    v1= 0.3898
    v2= 0.4083
    v3= 0.5462

    2. Relevant equations

    K= 1/2*m*v2

    p= m*v

    Percentage of change 1 - (kinetic before/kinetic after)

    percentage of change momentum 1 - (momentum before/momentum after)

    3. The attempt at a solution

    (.013925671/0.015474070) = .89999 so 90% is conservered a 10% change

    (0.01527887/0.017159564) = .890 so 89% is conserved a 11% change

    (0.027342351/0.032544623) = .840 so 86% is conserved a 14% change

    It seemed that the larger the velocity the more kinetic energy is lost. I am worried my conclusion is completely inaccurate.
  2. jcsd
  3. Nov 20, 2008 #2


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    Do you think your situation is perfectly elastic?
  4. Nov 21, 2008 #3
    I suppose its supposed to be since its a frictionless surface.
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