Acceleration vs Time Find Velocity

[circuscircus]

Homework Statement

The graph shows acceleration versus time of a particle moving along the x axis. Its initial velocity is 8m/s at t=0. What is the particle's velopcity at t=4s?

http://img259.imageshack.us/img259/6684/graphcc9.jpg

Homework Equations

The Attempt at a Solution

vi=8
ti=0
vf=??
tf=4

I was thinking of integrating y=-x+4 but I don't think I'm suppose to do that and also I don't know how to find +c.

 

[learningphysics]

What does the area under an a-t graph represent?

 

[circuscircus]

What does the area under an a-t graph represent?

Well integrating the acceleration gets you velocity, does it not?

 

[robphy]

I was thinking of integrating y=-x+4 but I don't think I'm suppose to do that and also I don't know how to find +c.

You don't really want to integrate "y=-x+4"... with those variables.
When you integrate the function with the appropriate physical variables, what is the physical interpretation of your "c" constant of integration?

You don't need to actually do the integral [with calculus]... you can do it geometrically using learningphysics' suggestion.

 

[circuscircus]

Well the area under the chart is 8 at 4 seconds but that's the vi so how doe sthat come into play?

 

[robphy]

Well the area under the chart is 8 at 4 seconds but that's the vi so how doe sthat come into play?

Try your integration method, as well.
Now, rethink your answer.

 

[Kushal]

correct me if I'm wrong, but i believe the equation v=u+at can be used, since this is a linear graph??

you know, u(initial velocity), and the product (at) is 0. the initial velocity is equal to the final velocity.