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Homework Help: Finding velocities in F vs x graph

  1. Jun 23, 2010 #1
    1. The problem statement, all variables and given/known data
    A object of mass 3.00 kg is subject to a force Fx that varies with position as in the figure below.

    Find the work done by the force on the object as it moves as follows:
    (a) from x = 0 to x = 4.00 m
    (b) from x = 5.00 m to x = 10.0 m
    (c) from x = 11.0 m to x = 15.0 m.
    (d) If the object has a speed of 0.500 m/s at x = 0, find:
    speed at x = 5.00 m
    speed at x = 15.0 m

    3. The attempt at a solution
    a. W=2.5N (4m) / 2 = 5J
    b. W=3N (5m) = 15J
    c. W=2.5N (4m) / 2 = 5J
    d. W=1/2 mv2 - 1/2 mvo2

    x=5m 15J = 3kg v - (3kg)(0.500m/s)
    v=2.29 m/s

    x=15m 0=3kg v - (3kg)(0.500m/s)
    v=0.5 m/s
    Last edited: Jun 23, 2010
  2. jcsd
  3. Jun 23, 2010 #2


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    I would not use 2.5 N for the force. I suggest that you find an equation for the straight line in the form F = mx and calculate the force at 5 m.
    Looks good.
    Same comment as part (a)
    What happened to the 1/2 and the square of the speed in the expressions above?
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