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Homework Help: Newbie needs help

  1. Sep 12, 2007 #1
    First, let me say I am new to the forums and new to physics, so if I do something wrong I apologize.
    1. The problem statement, all variables and given/known data
    Consider the 2 vectors
    A=4i -3j and B = -1i - 5j

    a) Calculate A +B
    b) Calculate A-B
    c) Calculate |A+B|
    d) Calculate |A-B|

    3. The attempt at a solution

    I easily determined a and b, however c and d are giving me dificulty since I dont exactly know how the absolute value affects the vectors. Any help would be much appreciated - Newb
  2. jcsd
  3. Sep 12, 2007 #2
    It means that you turn the vectors into positive values and add or subtract the value of the magnitude stick, which I can't remember the name of.
  4. Sep 12, 2007 #3
    I was wrong. I didn't check the notation properly. c and d are finding the absolute value of the difference between the vectors. So just subtract / add them normally, and find the hypotenuse of the resultant triangle.
  5. Sep 12, 2007 #4


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    Homework Helper
    Gold Member

    In this case, the bars mean the length of the vector inside. So for c), the problem is asking for the length of the vector that is the vector sum of A and B. For b), the problem is asking for the length of the vector that is the vector difference of A and B.

    Does this help?
  6. Sep 13, 2007 #5
    Still confused..lol,
    a) 3i + -8j
    b) 5i +2j
    That part I get
    is this how to do it?(just like you would use a normal abs value?)
    c) |4i+-1i|=|3i| and |-3j+-5j|=|-8j|= 8j
    making the FINAL answer 3i+8j
    and if that is correct is
    d) |4i--1i|=|5i| and |-3j--5j|=|2j|
    making that FINAL answer 5i+2j

    is this right?
  7. Sep 13, 2007 #6
    C and D are asking for the resultant magnitude of the vectors, so that means that you take those x and y components, and then calculate the hypotenuse of the triangle that they form. Pythagorean theorem, just do this ((I + I)^2 + (J + J)^2)^(1/2) that that is the answer to C. Magnitude is a scalar, while all of the components are vectors.
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