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!

Particle on a position vector.

  1. Feb 25, 2015 #1

    Yam

    User Avatar

    1. The problem statement, all variables and given/known data
    A particle moves in a plane described by the position vector r (t)= ( 2bsin( wt ))i + ( bcos( wt ) )j
    where b and w are some constants. The angle between its velocity and acceleration vectors at time t=(π/2w)

    a) is approximately 27 degree .
    b) is exactly 45 degree .
    c) is approximately 63 degree .
    d) is exactly 90 degree .
    e) cannot be determined since b and w are not specified.

    2. Relevant equations
    differentiation

    3. The attempt at a solution
    v(t) = (2bw(cos(wt)))i + (-bw(sin(wt))j
    a(t) = (-2bww(sin(wt)))i + (-bww(cos(wt)))j

    After that, how do i find the angles?
     

    Attached Files:

  2. jcsd
  3. Feb 25, 2015 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    How would you normally find the angle between two vectors?
     
  4. Feb 25, 2015 #3

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    What do you know about the dot product of two vectors?
     
  5. Feb 25, 2015 #4

    Yam

    User Avatar

    I see, the dot product would represent the angle between 2 vectors. Gimme some time to work the exact solution out
     
  6. Feb 26, 2015 #5

    Yam

    User Avatar

    Hi, is this formula correct? Or is this only for coordinates only?

    So, the solution is Cos-1(0)=90 degrees?
     

    Attached Files:

    • 45.gif
      45.gif
      File size:
      622 bytes
      Views:
      99
    Last edited: Feb 26, 2015
  7. Feb 26, 2015 #6

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    That's the right formula, but how do you get 0 for the dot product?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted