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!

Vectors vector

  1. Jul 28, 2015 #1

    Jec

    User Avatar

    Can someone help me how can I solve parts E and F ?
     

    Attached Files:

  2. jcsd
  3. Jul 28, 2015 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    Are you sure about your answer to d)? Seems to me that the three components of ##\vec r## are roughly equal, so I would not have expected the angle to be so close to 90 degrees.
    For e), you may have been shown a formula for finding the component of one vector in the direction of another. If not, try answering these two questions and comparing the answers:
    If you wanted the vertical component of a force F at angle theta to the vertical, what would it be?
    If you took the dot product of two vectors of magnitudes a, b, with angle theta between them, what value would you get?
     
  4. Jul 28, 2015 #3

    Jec

    User Avatar

    Uhm i tried to solve again for the angle and I got 123.06 degrees but not sure.
    Should I use only dot product ? would it be (6.1)(-1)+(9.4)(2)+(-8.9)(3) only?
     
  5. Jul 28, 2015 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    123 degrees sounds more ressonable. If you want me to check it exactly please post all your working.
    The answer to d) is not simply a matter of taking the dot product. Please try to answer the two questions I asked.
     
  6. Aug 10, 2015 #5

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    It is useful to know that, for any vector [itex]a\vec{i}+ b\vec{j}+ c\vec{k}[/itex], the components of the unit vector in that direction, [itex](a/d)\vec{i}+ (b/d)\vec{j}+ (c/d)\vec{k}[/itex], where [itex]d= \sqrt{a^2+ b^2+ c^2}[/itex], are the "direction cosines" of the vector: a/d is the cosine of the angle between the vector and the x-axis, b/d is the cosine of the angle between the vector and the y-axis, and c/d is the cosine of the angle between the vector and the z-axis.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Vectors vector
Loading...