VERY simple Velocity vs time graph interpretation

[seanistic]

Wow, I'm extremely frustrated with this one.

Homework Statement

http://img262.imageshack.us/img262/4616/probre1.jpg

I forgot to label the axis's. The X is time and the Y is Velocity

The Attempt at a Solution

Iv done a few things on this one:

First, I figured I would just count the area under it but I submitted the answer and it was wrong

Second, I used x = x(o) + v(o)t plugging in the velocity and time from the graph along with the x(o) which is given in the problem

Any help is appriciated, Thank You

 

[Feldoh]

You have to find the area under the curve to find position.

If you can't maybe this will help: http://img230.imageshack.us/img230/513/17914212vr1.jpg

 

[seanistic]

See, I did that and counted the area under the positive area in the first quadrant and then I subtracted it from the negative area in the 4th quad. I got 29 for the positive area and 6 for the negative, giving me 23 and it was wrong. So I figured maybe I had to add the areas for 35 but that as well came out wrong.

 

[Rainbow Child]

23m is the displacement. You are asked for the position.

 

[seanistic]

ughh, 1 more hint, I am not getting it

 

[Rainbow Child]

If the initial position is $x(0)=-10 m$ and the displacement is 15 m, what's the final position?

 

[seanistic]

x(0) is 10. I'm confused how the position is different from the displacement. I know the displacement is how far away it is from the orgin no matter how it travels but the position would be. I'm just not seeing it .

 

[Rainbow Child]

You are initial at $x(0)=10 m$. If your displacement $\Delta x$ is -10 m you should arrive to the origin.

$$\Delta x=x_f-x_i\Rightarrow x_f=\Delta x+x_i$$

Do you understand that?

 

[seanistic]

I'm sorry, This isn't making sense to me, I'm usually good with graph interpretation.

 

[Rainbow Child]

Ok, let's try this.

The initial position is 12 m. You walk 4 m at the positive direction. What is your displacement and what is your final position?

 

[seanistic]

displacement would be 4 m and your final position is 16 m. I see where your going with this so I would simply add my displacement to the initial position? make the answer 33?

 

[Rainbow Child]

Correct!

 

[seanistic]

You know what it was? I was thinking of the X axis as if it were distance even though I KNEW it was time. Because of this I was thinking its position was at 9 and from the initial position it would be -1 m . DUHHH. Thanks so much for your help.

 

[Rainbow Child]

Always it helps if you draw a picture o the actuall movement!
Glad I helped!

 

[Feldoh]

When you take the area under a curve you're finding the change in what ever quantity you're asked for. You need some sort of condition if you want to find the exact value. Without knowing that x(0) = 10m the best you could say about the graph would be the object moved 23m but I can't tell you EXACTLY where it is or EXACTLY where is started. Does that make sense?