physics finding kinetic energy

Discussion in 'Homework Help' started by zelda1850, Feb 21, 2010.

  1. zelda1850

    Thread Starter New Member

    Jan 3, 2010
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    a 20 kilogram block is placed at the top of a 10 meter long inclined plane. the block starts from rest and slides without friction down the length of the incline

    determines the kinetic energy of the block just as it reaches the bottom of the incline

    mass = 20 kg
    distance = 10 m
    height = 10 m

    the forumla is ke = 1/2 mv square

    but i dont have velocity what is the other forumla i can use to solve this problem?
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Find the slope of the inclined plane and then the analyse the weight of the block into its x-y components The x component is should be in parallel with the inclined plane. Use the x component to find the final velocity of the block and thus its kinetic energy.
     
  3. someonesdad

    Senior Member

    Jul 7, 2009
    1,585
    141
    Before worrying about what formulas to use, go back and read your textbook to understand the principles involved first. Read about conservation of energy, kinetic energy, and potential energy. You should then be able to make a statement about what principles are involved here. Once those principles are clear in your mind, the solution is pretty obvious and involves only a couple of simple formulas.

    Because there's no friction, the mechanical energies are conserved. If you've studied potential energy, consider the change in potential energy of the block and how it might be related to the kinetic energy of the block.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,148
    1,791
    There appears to be a misprint. The inclined plan cannot be 10 m long (the hypotenuse) and 10 m high (one of the sides). That would make it a vertical wall and not an inclined plane.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Maybe it does not mean the length of the inclined level itself but its base length.
     
  6. Papabravo

    Expert

    Feb 24, 2006
    10,148
    1,791
    Plausible. The OP needs to clarify the original question.
     
  7. Heavydoody

    Active Member

    Jul 31, 2009
    140
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    Does the length of the ramp matter in this situation?
     
  8. mik3

    Senior Member

    Feb 4, 2008
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    Yes, that is a good point. The length does not really matters, it is the height that matters as to calculate the potential energy of the block. Then the kinetic energy at the end of the incline equals the potential energy assuming no friction.

    Good point Heavydoody. :)
     
  9. Heavydoody

    Active Member

    Jul 31, 2009
    140
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    One of the benefits of frictionless ramps and drag-free objects...unfortunately, they seem to be somewhat rare...well, except in physics textbooks ;)
     
  10. zelda1850

    Thread Starter New Member

    Jan 3, 2010
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    0
    oppps i forgot to add that there was a picture with the question showing that the height was 10 meters
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    Did you understand how to solve it?
     
  12. zelda1850

    Thread Starter New Member

    Jan 3, 2010
    18
    0
    nope is their a formula?
     
  13. Heavydoody

    Active Member

    Jul 31, 2009
    140
    11
    In an isolated system with only conservative forces,
    ΔK+ΔU=0.
     
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