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Homework Help: Kinetic energy and work energy thereom

  1. Sep 26, 2008 #1
    a 5.75 kg object is initially moving so that its x-component of velocity is 6.00m/s and its y-component is -2.00m/s. what is the kinetic energy of the object at this time. What is the change of kinetic energy do that its velocity is 8.50m/s in the x direction and 5.00m/s in the y direction
  2. jcsd
  3. Sep 26, 2008 #2
    kinetic energy equals (1/2)m*v^2
    You already know the mass and the 2 components of velocity, just use pythagorean theorem to find the actual velocity.

    and since mass can't change, then change in kinetic energy is equal to (1/2)m*(change in velocity)^2
  4. Sep 26, 2008 #3
    As perillux said, you use the pythagorean theorem to find the total velocity magnitude and use that and the given mass in the formula to get the answer.
  5. Sep 27, 2008 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Careful. This is incorrect.

    [tex]\Delta {KE} = 1/2m\Delta(v^2) \ne 1/2m(\Delta v)^2[/tex]
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