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Homework Help: Basic vector questions

  1. Aug 21, 2010 #1
    1. The problem statement, all variables and given/known data

    Which of the following are vectors? (Select all that apply.)
    a] ‹ 0.7, 0.7, -0.7 ›
    b] ‹ 0, 2.3, -1 ›
    c] 0
    d] 5׋ 33, 1.04, -9.5 ›
    e] −3×10−6
    f] 3.5

    Which of the following are vectors? (Select all that apply.)
    a] a-> (the arrow is above the a)
    b] r->/2
    c] |r->|
    d] 10r->
    e] ‹ rx, ry, rz ›
    f] r

    2. Relevant equations
    A vector has a magnitude and direction.

    3. The attempt at a solution
    I originally choose a and b because those are in the form that I'm familiar with...that of a position vector. However, this homework assignment is online and apparently those two are not correct. I then tried a,b, and d, since d (from what I can tell) is just a scalar multiplied by a vector...the answer of which is indeed a vector as well, but that wasn't right either. I think that c, e, and f are scalars. I really have no idea why the answers I gave are not correct, and would appreciate it if someone could shed some light on my errors.

    For the second problem, I thought that the answer would have been a and e. C is obviously the magnitude, and b & d are multiplied by a scalar. F is just a scalar, too. But as I decided in the first problem, multiplying a scalar by a vector just makes a vector. So I suppose I need to try a,b,d,and e?

    I'm feeling PRETTY dumb right now, since this is the homework after the first night. Encouragement as well as help would be greatly appreciated.
    Last edited: Aug 21, 2010
  2. jcsd
  3. Aug 21, 2010 #2
    First off, I will confirm that a b and d are vectors, as you've determined.

    I think e is also a vector, because it is negative. It has a magnitude of 3x10-6 and an angle of 180 degrees. However, I'm pretty sure scalars can be negative technically. It'd be kind of silly if that is what this question hinged on.

    for the second one, from what you're describing, I'd choose abde too. Is the r in the last one in bold? That is another notation for a vector, meaning it could be one if you didn't present it correctly.
  4. Aug 21, 2010 #3
    I don't see how e being negative makes it a vector..it still only has one component. I was under the impression that you at least need to know what it represents, i.e. it could be <−3×10−6 ,0> and that'd be a vector, but since it doesn't have the second place holder (y) in my example, it's just a scalar.
  5. Aug 21, 2010 #4
    I wouldn't worry about it too much. Those questions are over notation. If I told you {A|} is a "meh", you would know that {A|} stands for "meh", but what is "meh"? In the same sense if you didn't know what a vector was before the notation was introduced, then telling you the notation would have been pointless. My point is is that notation is somewhat important but it is not the main focus, the main focus is on the concepts.

    That being said are any of the choices bolded or have a line (as opposed to an arrow) over the top of them? Both of these also tend to represent vectors. Also some people will just write 0 and call it a vector as a shorthand way of writing (0, 0, 0, ...)
  6. Aug 21, 2010 #5
    Sorry guys. It was a technical error. I got the questions right with my original reasoning. I now feel better about beginning my college physics career. :)

    Edit-Feldoh, that's what I was thinking too, but since I never took physics in high school, I've gotta learn everything from the bottom to the top. It's really helped me to read two different accounts, rather than just the textbook.
  7. Aug 21, 2010 #6
    Actually that could be a vector, maybe.

    -3 x 10^-6 has a magnitude of 3 x 10^-6 at an angle of 180 (direction)
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