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!

Homework Help: Adding magnitude of vector

  1. May 27, 2009 #1
    1. The problem statement, all variables and given/known data

    A vector of magnitude 20 is added to a vector of magnitude 25. The magnitude of this sum might be:
    A. Zero
    B. 3
    C. 12
    D. 47
    E. 50

    2. Relevant equations

    Probable the Pythagoreans and use of sin, cos, etc.

    3. The attempt at a solution

    Not sure how to add the magnitude of vector w/out knowing the angle or the different components.

    Thanks for looking at the problem.
  2. jcsd
  3. May 27, 2009 #2


    User Avatar
    Homework Helper

    Welcome to PF.

    Maybe eliminate the answers that aren't possible?
  4. May 27, 2009 #3
    I know what the answer it. I just don't know how the answer key got there. There are some rules that constrain the addition/subtraction of magnitude of vectors, but I don't know what they are. I am searching the net but to no avail.

    Thanks for the welcome.
  5. May 27, 2009 #4


    User Avatar
    Homework Helper

    If you have those two force acting on a body, when would the resultant force be maximum and when would they be minimum?
  6. May 27, 2009 #5


    User Avatar
    Homework Helper

    You know that depending on direction a vector can be added head to tail right? So the biggest value the result can be is ... |20| + |25|

    Likewise the smallest value the result can be is when they are in opposite directions. |25| - |20|

    Looks like there is only one answer that satisfies these conditions.
  7. May 29, 2009 #6

    Yea, this was the rule I was looking for. Thanks a lot Pion.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook