Solving Physics Motion: When Does Green VAN Overtake Red CAR?

[Hollysmoke]

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

 

[marlon]

That's correct

marlon

 

[Hollysmoke]

I'm just lost on how to start the question...my friend and I are discussing it but bleh >_<

 

[marlon]

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

 

[Hollysmoke]

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.

 

[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.

i don't think you are getting the point.

Just set up v = a*t

by using $$y-y1 = \frac{y2-y1}{x2-x2}(x-x1)$$

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

 

[Hollysmoke]

Omg I Figured It Out. Thank You Marlon!