Position Vector Question

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 ?
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 Mentor Blog Entries: 1 The units are not km/h, the units are that of km/h*t = Length/time * time = length.
 ok, i see it now, thanks

Position Vector Question

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?

Thanks!

Mentor
Blog Entries: 1
 Quote by Caldo120 I do not understand why the sin is negative though. Could anyone run through the differentiation of this?
You're asking where the minus sign comes in when finding d(cosx)/dx? Have you studied calculus?

Try: Differentiation of trigonometric functions
 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!

 Tags dimension, position, vector, velocity