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Homework Help: Integral for displacement from velocity

  1. Jan 29, 2013 #1
    1. The problem statement, all variables and given/known data
    An object is moving with a velocity by the equation

    v(t) = [(3/2)(m/s2)t] i^ + [(3/2)(m/s3)t2] j^

    What is the magnitude of displacement during 0 - 2s

    2. Relevant equations

    v(t) = [(3/2)(m/s2)t] i^ + [(3/2)(m/s3)t2] j^

    3. The attempt at a solution

    (3/2) ∫ from 0 to 2 [(t2 / 2) i^] + [t3/3]y^

    plug and chug with t = 2

    (3/2) √(squaring each of the i^ + j^)

    I end up with some decimal answer which I know is wrong. Where am I screwing up?
  2. jcsd
  3. Jan 29, 2013 #2
    Who says you're wrong. What do you get? Is it something like 6.5?
  4. Jan 30, 2013 #3
    When I plug in 6.5 to the online quiz it says sorry wrong answer, "Don't forget to add the components of a vector quadratically to determine it's magnitude." I don't understand where I'm going wrong. Help
    Last edited: Jan 30, 2013
  5. Jan 30, 2013 #4
    wait what about the units of s^2 and s^3????

    EDIT: I don't think that's it
    Last edited: Jan 30, 2013
  6. Jan 30, 2013 #5
    Oops. 6.5 was wrong. I must have made a mistake somewhere. Here are the correct results: What did you get for the two components of the displacement vector? I got 3 and 4 using your equation. They were 3/2 x 2, and 3/2 x 8/3. So the correct displacement magnitude must be 5.

    Sorry for any confusion I caused. It looks like you had it right all the way, but just made a mistake in arithmetic.

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