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: Velocity from position in a parametric

  1. Mar 29, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img21.imageshack.us/img21/7910/68588225.th.jpg [Broken]

    2. Relevant equations

    3. The attempt at a solution

    I know that the velocity is the derivative of the position vector.. but I am kind of confused how to do this
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Mar 29, 2009 #2
    How about graphing the table of values to start?
  4. Mar 29, 2009 #3
    I've done that as well... but from the graph I can't find the velocity
  5. Mar 29, 2009 #4
    You should have drawn two graphs (why?) and the velocity is the slope (why?).
  6. Mar 29, 2009 #5
    the velocity is the slope (why?).

    because it's the derivative of the graph...

    why two graph, I don't know
  7. Mar 29, 2009 #6
    You need 2 because you have 2 position components: x vs t and y vs t.
  8. Mar 29, 2009 #7
    ok, I got v = -4/5i + 5/5j, is this correct?

    if that's correct, how do I answer this one:

    Any time when the particle is moving parallel to the y-axis.
  9. Mar 29, 2009 #8
    I feel too lazy to verify that at moment. Just double-check the slope from each graph.

    This is where the x vs y graph comes into play. When would the particle by moving parallel to the y-axis in this graph? Hint: tangents.
  10. Mar 29, 2009 #9
    the graph looks really weird... it's like a circle
  11. Mar 29, 2009 #10
    Good. If it looks like a circle, there is a point where the tangent at that point is parallel to the y-axis. Do you agree?
  12. Mar 29, 2009 #11
    yes and that is at point x = 7 and y = 5.. which is at 7.5 sec

    how about:

    Any time when the particle has come to a stop?
  13. Mar 29, 2009 #12
    Hint: The particle is not moving when its velocity is 0.
  14. Mar 29, 2009 #13
    I got it now.. thanks for the help :)
    Last edited: Mar 29, 2009
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook