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Homework Help: Conservation of Energy error

  1. Nov 23, 2007 #1
    1. The problem statement, all variables and given/known data
    We did an experiment where A marble travels down a ramp,
    rolls along for 5 cm, then falls off a desk. The marble starts off
    while gravitational potencial energy, and ends with kinetic energy.
    We were given a formula for the distance from the desk the marble
    lands, 'x', calculated by multiplying the height of the ramp by the
    height the desk and square rooting the product. So here's my question:
    Why is the expected 'X' so different from the 'X' obtained in the experiment?

    2. Relevant equations
    Egpe = mgh
    Eke = 1/2mv**2

    3. The attempt at a solution

    Is the large percent error caused by the marble
    having some kinetic energy on the ramp?

    Jen DM
  2. jcsd
  3. Nov 24, 2007 #2

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    The formula for dist from the desk should be 2*sqrt(height of ramp*height of table), assuming no loss in energy for the 5 cm roll. You can deduce it quite easily.
  4. Nov 26, 2007 #3
    I know that that formula shows what should happen, but the results of the experiment show something 30% different, and I was wondering why they are so different, i(e sound energy present?)

    I appreciate your help :)

  5. Nov 26, 2007 #4

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    Your original formula didn't have the factor of 2. So, I thought that could be the reason for the discrepancy.

    The marble also has rolling KE, which it gains when it crosses the flat table, which should be the most significant factor. The formula deduced was for just a point mass sliding.

    Sound is emitted after the marble strikes the ground and is not relevant, unless of course you mean the sound when it hits the table and rolls across it. That should be very less.
  6. Nov 29, 2007 #5
    That makes sense, since the marble is rolling, not sliding down the ramp.

    thank you so much!
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