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Two boxes are on frictionless ramps (Speed and KE)

  1. Mar 17, 2009 #1
    1. The problem statement, all variables and given/known data
    Two boxes are resting on frictionless ramps. Box 1 is lighter and sits on a steep ramp while Box 2 is heavier and sits on ramp that is less steep. The boxes are released from the same point.

    Which box (if either) has
    a) The greater speed?
    b) The greater kinetic energy at B


    2. Relevant equations
    Box 1 = Lighter and steeper ramp
    Box 2 = Heaver and less steep ramp
    Initial starting point = A
    Displacement = B


    3. The attempt at a solution
    I'm sure its wrong. I don't really have a concise explanation.
    a) Box 1 should have the greater speed because gravity will produce a greater effect on a higher slope.
    b) Box 2 should have greater kinetic energy at B because it has more mass and thus can create higher momentum.
     
  2. jcsd
  3. Mar 17, 2009 #2

    Doc Al

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    Staff: Mentor

    Hint: Consider the fact that mechanical energy is conserved on the frictionless ramps. What can you deduce from that?
     
  4. Mar 17, 2009 #3
    Meaning there is no kinetic or potential energy present? So then neither box would be quicker than the other?
     
  5. Mar 17, 2009 #4

    Doc Al

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    Staff: Mentor

    :confused:

    What's the initial energy of each box? The final energy? How do the speeds compare?
     
  6. Mar 17, 2009 #5
    Hmm.. no initial energy? Marketing grad here boss, bear with me.. lol.
     
  7. Mar 17, 2009 #6

    Doc Al

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    Staff: Mentor

    Both boxes start out at some initial height (presumably the same for both boxes) so they have gravitational potential energy. What's the expression for gravitational PE as a function of height (with respect to the ground)?
     
  8. Mar 17, 2009 #7
    Work? F x D?
     
  9. Mar 17, 2009 #8
    Expression for Grav. Potential energy when the body is close to the earth?
     
  10. Mar 17, 2009 #9
    That is the work done by a constant force F over a displacement d.

    Think about the expression for grav. potential energy..
     
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