Thread: Physics question (elasticity)

  1. #1
    Unregistered Leeman_s's Avatar
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    Physics question (elasticity)

    What is the elasticity of a ball which hits a wall at 10 m/s and rebounds off the wall at 8 m/s? (answer to 2 significant digits)

    That's an online question for school. All of us trying to do it can't get it. It should be 80% I think, but it's not. And it's not a multiple choice question.

    Anyone know how you would do that?

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    Mayor of Awesometown Govtcheez's Avatar
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    5.

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    Unregistered Leeman_s's Avatar
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    What....? 5 is the answer? Huh? I can't make sense out of that...and it should be a two digit number (yes I know how sig figs work but I know that what my teacher implies by that)

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    64%

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    C++ Developer XSquared's Avatar
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    8.0x10^-1
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    C++ Developer XSquared's Avatar
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    Originally posted by ZerOrDie
    64%
    How'd you get that?
    Naturally I didn't feel inspired enough to read all the links for you, since I already slaved away for long hours under a blistering sun pressing the search button after typing four whole words! - Quzah

    You. Fetch me my copy of the Wall Street Journal. You two, fight to the death - Stewie

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    & the hat of GPL slaying Thantos's Avatar
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    3X


















    Now just have to solve for X.

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    Registered User Xei's Avatar
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    e = ( 1 - ((EKInitial - EKFinal) / EKInitial)) *100 = x%

    We will substitute any mass. Lets say 1kg.

    EK = (1/2)mv^2

    EKInitial = (1/2)(1)(10)^2 = 50J
    EKFinal = (1/2)(1)(8^2) = 32J

    ((50 - 32) / 50) * 100 = 36%

    1 - .36 = .64
    .64 * 100 = 64%

    The ball has an elasticity of 64% (as 36% of the Kinetic energy was lost). Just remember your conservation of energy.
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    looks like someone took the time to explain my answer lol

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    Registered User Xei's Avatar
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    Originally posted by ZerOrDie
    looks like someone took the time to explain my answer lol
    Yes. I had to look back on some previous work because I realized that I actually forgot how to calculate the elasticity of an object - which frusterated me to no end.
    "What are you after - the vague post of the week award?" - Salem
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    Unregistered Leeman_s's Avatar
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    im so mad. I even tried that, but it said it was incorrect so I reverted to 80%! I think it has problems with how you enter the answer, like it'd make a difference if it was 64, 64%, or 64 %

    That threw me off then, indeed!

  12. #12
    Registered User Xei's Avatar
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    Try .64
    "What are you after - the vague post of the week award?" - Salem
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