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Work and kinetic energy

  1. Mar 1, 2008 #1
    The magnitude of a certain one-dimensional force varies according to:

    F = 6.68x^2 + 1.56

    where x is the displacement from the origin in meters, and F is the force in Newtons. At t = 0, a 677 g mass is at the origin moving in the positive x-direction at speed 8.46 m/s when this force begins to act on it.
    ASSUME: there are no other forces acting on the mass.

    a) How much work is done by the force on the mass when it reaches x = 2.78 m?
    b) What is the speed of the mass when it reaches 2.78 m?


    i put x=2.78 into the equation. w=(6.68*2.78^2)*2.78
    and get the wrong answer.

    3. The attempt at a solution
  2. jcsd
  3. Mar 1, 2008 #2

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    If you put the value of x, you get the force, not the work. Think about what is work done in terms of force and distance.
  4. Mar 1, 2008 #3
    not, i put the value of x. and get the force, then use the force * distance.w=(6.68*2.78^2+1.56)*2.78
  5. Mar 1, 2008 #4

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    When the force is not constant, then the work done is Integral(from x1 to x2)[Fdx].
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