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Finding Work with velocity

  1. Oct 14, 2007 #1
    The only force acting on a 1.9 kg body as it moves along the positive x axis has an x component Fx = - 6x N, where x is in meters. The velocity of the body at x = 3.0 m is 8.0 m/s.

    (a) What is the velocity of the body at x = 4.0 m?

    well work is the integral of the f(x) function, so its -3x^2. Knowing that I can get the work done from x=3 to x=4. which is -3*9 and -3*16. after omitting the sign, which I figured I need to do after about an hour of this problem, I get a net change of 21J. so I plug that into 1/2MVf^2-1/2MVi^2 and get 1/2M(Vf^2-Vi^2)=21J


    this yields me an answer of 9.28 m/s
    I must have done this problem about 8 times now, and I cant get it right.

    (b) At what positive value of x will the body have a velocity of 5.0 m/s?
  2. jcsd
  3. Oct 14, 2007 #2
    Does the force begin to act the object where x=0?
  4. Oct 14, 2007 #3
    I don't really understand what you are trying to say?
  5. Nov 6, 2008 #4
    heyy f is in negative direction vfinal must be less than 8m/s
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