When does the green van overtake the red car?

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Hollysmoke
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I'm having trouble with the 2nd part of this question, which asks at what instant the VAN (Green) overtakes the CAR (Red). I drew out the diagram. From what I believe, the displacements have to be equal so would I have to substitute two equations in each other?

http://img371.imageshack.us/img371/4530/diag2nj.png
 
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I'm just lost on how to start the question...my friend and I are discussing it but bleh >_<
 
Well write down the equation of v as a function of time t.

You know that :
(30,15) and (0,0)
(60,20) and (0,0)

are the couples of points that belong to each linear curve.

Can you write down the equation of a linear function when these points have been given ?

marlon
 
well we're not supposed to use linear function...it's on agraph so it displacement would the area underneath the graph...still stuck on it.
 
Hollysmoke said:
well we're not supposed to use linear function...it's on agraph so it displacement would the area underneath the graph...still stuck on it.
i don't think you are getting the point.

Just set up v = a*t

by using [tex]y-y1 = \frac{y2-y1}{x2-x2}(x-x1)[/tex]

The (x1,y1) and (x2,y2) have been given. Keep in mind that x is t and y is v here

Or you can indeed get the a by calculating the surface under the curve.

Anyhow, the result must stay the same.

marlon