1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding the magnitude of a vector B given vector C

  1. Sep 9, 2015 #1
    1. The problem statement, all variables and given/known data

    If vector B is added to vector C = 3.7i + 2.4j, the result is a vector in the positive direction of the y axis, with a magnitude equal to that of vector C. What is the magnitude of vector B?

    2. Relevant equations
    sqroot(a^2x+a^2y) = a

    3. The attempt at a solution
    My line of reasoning: since the magnitude of vector B is equal to the magnitude of vector C, then finding the magnitude of vector C using the given components would yield the magnitude of vector B.

    How I went about solving the problem:

    I used 3.7i as the x component of C and 2.4j as the Y component, then plugged each component into the following formula: c = sqroot(c2x+c2y). I received an answer of 4.4 but it has been marked as incorrect.

    Please let me know why my reasoning is incorrect (I don't need the answer).
  2. jcsd
  3. Sep 9, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    Hello Cada, welcome to PF :smile: !

    Did you make a drawing of the situation ?
  4. Sep 9, 2015 #3

    Thanks for replying. No, I had not created an illustration of the situation at the time since I did not believe it would be necessary for this question.

    I created one just now but I still do not see how it will help yield the magnitude of vector C.

    Here is the drawing: http://i60.tinypic.com/2zrf6og.jpg

    Attached Files:

    • Vec.jpg
      File size:
      46.4 KB
  5. Sep 9, 2015 #4
    If the x component of the resultant is equal to zero, what does the x component of B have to be?

  6. Sep 9, 2015 #5

    Apologies.. I am reading the question incorrectly therefore assuming that the magnitude of vector B is equal to that of vector C when this is not the case.

    I will give this another go - thank you for suggesting to draw this and helping.
  7. Sep 9, 2015 #6


    User Avatar
    Science Advisor
    Homework Helper
    2017 Award

    Dear Cad,

    In the picture it is hard to imagine you made the magnitude of ##\vec a## equal to the magnitude of ##\vec c##. -- Ah, you've got it! See that making a picture helps out ?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted