1. Not finding help here? Sign up for a free 30min 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!

Question: scalars from vectors

  1. Sep 15, 2004 #1
    I saw this question posted yesterday, and now got a similar question to work out.

    A = (6i-8j) cm
    B = (-8i+3j) cm
    C = (26i+19j) cm

    aA+bB+C=0

    Determine the two scalars a and b.

    Ideas anyone??

    Thanks

    Dora
     
    Last edited: Sep 15, 2004
  2. jcsd
  3. Sep 15, 2004 #2
    C=0 ?? But you jsut said C=26i+19j . Is this a typo? or did you mean aA+bB-C=0

    in which case aA+bB=C
    seems pretty straightforward to me. Split it up into the vector components, and youll have 2 equations with 2 unknowns, easily solveable.
     
  4. Sep 15, 2004 #3
    Sorry. That was a tipo. I made a mistake.

    aA+bB+C=0 not aA+bB=C=0 not
     
  5. Sep 15, 2004 #4
    Well, what have you done so far? How have you approached it?
     
  6. Sep 15, 2004 #5
    I used the equation a^2 + b^2 = c^2 and the coodinates (6,-8) and (-8,3) to determine that the magnitude of A is 0.5cm and that the magnitude of B is 0.7cm. But I don't know if that is what is meant by "determine the two scalars a and b". I'm asuming scalars in this question is the scalar quantity or "magnitude".
     
    Last edited: Sep 15, 2004
  7. Sep 15, 2004 #6

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    The "equation a^2+ b^2= c^2" doesn't even make sense here. You are given vectors A, B, C, not numbers a, b, c (and you certainly don't have any number c).

    Do you know how to add vectors and multiply vectors by a number? That should have been ther first thing you learned!

    If A= 6i+8j, then aA= (6a)i+ (8a)j.

    If B= -8i+ 3j, then bB= (-8b)i+ (3b)j

    aA+ bB = (6a- 8b)i+ (8a+ 3b)j and that must be equal to C= 26i+ 19j.

    Okay, have you learned that two vectors are equal only if the respective components are equal?

    To have aA+ bB= C, you must have (6a- 8b)i+ (8a+ 3b)j= 26i+ 19j and so
    6a- 8b= 26 and -8a+ 3b= 19.

    Can you solve those two equations for a and b?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Question: scalars from vectors
  1. Vector and scalars (Replies: 2)

Loading...