Kinematics Car velocity Problem

[hiineko]

Homework Statement

In the figure here, a red car and a green car move toward each other in adjacent lanes and parallel to an x axis. At time t = 0, the red car is at xr = 0 and the green car is at xg = 223 m. If the red car has a constant velocity of 20.0 km/h, the cars pass each other at x = 43.1 m. On the other hand, if the red car has a constant velocity of 40.0 km/h, they pass each other atx = 76.9 m. What are (a) the initial velocity and (b) the (constant) acceleration of the green car? Include the signs.

Homework Equations

[/B]

The Attempt at a Solution

eq 1 = 179.9=Vo(7.75)+1/2a(7.75)^2
eq 2 = 146.1=Vo(6.92)+1/2a(6.92)^2

insert 2 to 1

Vo = 146.1-1/2a(6.92)/(6.92)

179.9=(146.1-1/2a(6.92)/(6.92))(7.75)+1/2a(7.75)^2

got a = 5.06 m/s^2
and vo as 3.60

is my answer right?

 

[mfb]

You could explain where all those numbers in equation 1 and 2 come from, that makes it easier to understand the solution.
Did you plug the result back into those equations to check?

 

[hiineko]

You could explain where all those numbers in equation 1 and 2 come from, that makes it easier to understand the solution.
Did you plug the result back into those equations to check?

Vr = 20km/h = 5.56m/s x = 43.1
v=d/t -> t=d/v = 43.1/5.56=7.75s
xgreencar - x = 223 - 43.1 = 179.9

179.9=vo(7.75)+1/2a(7.75)^2

same procedure to eq. 2

Sorry but I need a bit help here
*is my answer right
*if not, can you please help me?

 

[mfb]

I suggested a way you can test your answer yourself.

Yes it is right. Well, several units are missing.

Edit: oh right, forgot about the signs.

 

[insightful]

Check signs per original problem statement.

 

[hiineko]

I suggested a way you can test your answer yourself.

Yes it is right. Well, several units are missing.

Edit: oh right, forgot about the signs.

That's one thing that bothers me I need signs how do I know what signs will I use? I just got a positive does it mean I'll use + sign?

 

[insightful]

That's one thing that bothers me I need signs how do I know what signs will I use? I just got a positive does it mean I'll use + sign?

On the X axis,which way is the green car going?

 

[hiineko]

On the X axis,which way is the green car going?

So 5.06 and 3.61 will be put a - sign on it? If that's what you meant

 

[insightful]

Correct, if velocity and acceleration are in the (defined) negative direction, they will have negative values.

 

[hiineko]

Correct, if velocity and acceleration are in the (defined) negative direction, they will have negative values.

Okay thank you! Off to my next question in my next post see you there lol kidding Thankyouu