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!

Position Vector Question

  1. Oct 8, 2008 #1
    My problem is not so much the mathematics of doing the question, but rather the units.

    The question states: "A car travels across a hilly landscape with a position vector given in the x - z plane.

    Position Vector = 30 km/hti + 1 km cos (t/(0.1h))k

    How can the units for a position vector be given as km/h ?
  2. jcsd
  3. Oct 8, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The units are not km/h, the units are that of km/h*t = Length/time * time = length.
  4. Oct 8, 2008 #3
    ok, i see it now, thanks
  5. Oct 3, 2010 #4
    I'm struggling with the maths side of this question. I've done some searching and came across an answer of v(t) = i30 - k10sin10t and I kind of understand this. I do not understand why the sin is negative though. Could anyone run through the differentiation of this?

  6. Oct 3, 2010 #5

    Doc Al

    User Avatar

    Staff: Mentor

    You're asking where the minus sign comes in when finding d(cosx)/dx? Have you studied calculus?

    Try: http://en.wikipedia.org/wiki/Differentiation_of_trigonometric_functions" [Broken]
    Last edited by a moderator: May 5, 2017
  7. Oct 3, 2010 #6
    oh dear. apologies. I was flicking through my table of "INTEGRALS" and wondering why it didn't make sense. Thoroughly embarrassed.

    Thank you though for showing me I must pay more attention!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Position Vector Question
  1. Vector positions (Replies: 1)

  2. Position Vector (Replies: 4)