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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

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    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

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    Staff: Mentor

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

    Try: Differentiation of trigonometric functions
  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!
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