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Homework Help: Why use unit vector for this, and not for that?

  1. Feb 11, 2009 #1
    the car problem in my text uses the unit vector, and the second one doesn't...

    how come?


  2. jcsd
  3. Feb 11, 2009 #2


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    The second problem is more complex and requires vectors to take care of the 3 directions involved. The first (car) problem has only one direction so no need for vectors.
  4. Feb 11, 2009 #3
    but it did the opposite of just that.

    the car used 'unit' vector....

    while the second does not use the 'unit' vector
  5. Feb 12, 2009 #4
    The first problem is asking for a moment about an axis. I'm pretty sure this is why you have to employ the unit vector in your calculations. If i recall correctly (been awhile since I was in statics) the unit vector here will be j or [0i 1j 0k]. Is that familiar?

    The second problem is asking for a moment about a point.
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