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Homework Help: Vectors and Motion

  1. Sep 14, 2013 #1
    For the following motion diagrams, draw an arrow to indicate the displacement vector between the initial and final positions.
    a)0 is at the top right and drops off to the left gradually to 5
    b)starts at 0 at the bottom right and raises up to form the maximum of a parabola and start a decent down for 2 seconds.
    c)Looks like a v with 0 in the upper right hand corner going down to 3 and then up again to 6.

    I'm not quite sure how to do these. I understand that vectors usually have magnitude and direction as they are vector quantities. But do I just draw an arrow from 0 to the last point with an arrow pointing at that last point? We only briefly went over vectors in our hour long lecture.

    There's another problem dealing with adding vectors. I know how to do them, but the instructions are:
    Draw and label the vector sum A+B.
    I got the first two, but the last problem has the vectors going in opposite directions and of equal magnitude (there's no quantity given). How in the world would you draw such a thing. I mean the net force would be 0 and therefore not have a vector direction or magnitude it would just stay still. So do I just not draw anything?
  2. jcsd
  3. Sep 14, 2013 #2
    It could be just me, but I am confused by your descriptions. Is there any way at all you could post the diagrams rather than describing them?
  4. Sep 15, 2013 #3
    Problem 19, all parts are what I'm having trouble on. I figure if I can get those down 20 should come fairly easily.

    I've drawn my best guesses as to what I'm to do.
    I'm having a rough time doing the homework for this class as we maybe have anywhere from 30min to an hour discussion and then we jump into a lab each class. I feel it's counterproductive for a lot of things. It's hard to just cover "basic" material and then move on with life.
  5. Sep 15, 2013 #4


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    Staff: Mentor

    Yes, the displacement vector is simply the vector that runs directly from the starting point to the finishing point, regardless of the path in between.

    What geometric object has zero length or size, and no direction?
  6. Sep 15, 2013 #5
    Thank you, I just came to that assumption myself about 19.

    I don't know. If it has no size it shouldn't exist right? An object being pulled in opposite directions at equal force would do nothing. Maybe I'm not understanding your question. Edit: An undefined object?

    I mean A+B of equal magnitude in opposite directions could be viewed as A+(-A), as the vector is in reverse direction which is what multiplying by a negative one would accomplish. So it would be 0...
    Last edited: Sep 15, 2013
  7. Sep 15, 2013 #6
    http://mathinsight.org/site_media/image/image/vector_opposite.png [Broken]
    If I drew the sum of the vectors like this would that be technically correct? Or am I missing it entirely.
    Last edited by a moderator: May 6, 2017
  8. Sep 15, 2013 #7


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    Staff: Mentor

    Hint: look at the end of most sentences. :wink:

    I've never actually assigned (or had to do) a problem like that, which basically meant "draw a zero vector", so I can't swear that's what they're looking for, but that's how I'd do it. Of course, what we can actually draw is only an approximation.
  9. Sep 15, 2013 #8
    I see what you're getting at there. :P

    Yea it's a little confusing, especially for just starting out with vectors. But I guess a period is the best representation of signifying zero. I feel for all intents and purposes I could just leave it blank and technically be correct, but I don't think the teacher would like that very much. I guess an explanation of what is going on could help.

    Thank you for your assistance. I have many more questions, but I'm trying to get through the chapter before making too many more posts.
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