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Homework Help: Physics Problem find displacement.

  1. Sep 8, 2007 #1
    1. The problem statement, all variables and given/known data A duck has a mass of 2.5 kg. As the duck paddles, a force of the water exerts a force of 20.0 N in a direction of 52 degrees south of east. When these forces begin to act, the velocity of the duck is .11 m/s in a direction due east. Find the magnitude and direction ( relative to due east) of the displacement that the duck undergoes 3.0 s while the forces are acting.

    angle=52 degrees
    F=.20 N
    Mass of duck=2.5 kg

    2. Relevant equations
    Acos 52 degrees
    A sin 52 degrees

    x=Vox(t) + Ax (t)^2/ 2

    3. The attempt at a solution

    I figured out the x component, and I got .20cos 52=.123 N
    Then I added .10 N + .123 =.223 N
    Then I figured out the acceleration .233 N/ 2.5 kg= .089 m/s^2
    (if your getting a different answer then me it's because I rounded off, but I'm still using the exact numbers on my calculator such as

    Then I used that kinematic equation x= .11 m/s (3.0 s) + (.089 m/s^2) (3.0s)^2/2 = .7305 m

    In the back of my book the answer is .78 meters. What did I do wrong.
  2. jcsd
  3. Sep 8, 2007 #2

    Doc Al

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    Staff: Mentor

    Your solution is a bit hard to follow. Try solving for the x (east) and y (north) components separately. Find the components of the force, then the acceleration. Then solve for the displacement components, then the total displacement.
  4. Sep 8, 2007 #3
    Components of the force
  5. Sep 8, 2007 #4


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    Homework Helper

    The question mentions 20N. But you use 0.20N and 0.10N... I assume the 0.20 is a typo but where is the 0.10 coming from?
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