# Homework Help: Physics poof

1. Feb 24, 2008

### chocolatelover

1. The problem statement, all variables and given/known data

Prove that if the acceleration is constant, the average velocity=vf+vi/2

2. Relevant equations
average velocity=xf-xi/change in t
xf=xi+vit+1/2at^2
vf^2=vi^2+2a(xf-xi)

3. The attempt at a solution

I started out by drawing a diagram:

_ _ _ _ _ _ _ _ _
Vi v vf
20km/h 20km/h

20+20/2=20

Do you think this proves it or is there another way of doing it?

Thank you in advance

2. Feb 25, 2008

### chocolatelover

Thank you very much

3. Feb 25, 2008

### qspeechc

Can you use calculus or not?

4. Feb 25, 2008

### qspeechc

vf = vi + at
Now if a=constant, the graph of velocity plotted against time is a straight line, yes? (From the equation above)
Now it is obvious that the average velocity between vf and vi must be (vf + vi)/2 from the graph.
Otherwise you can use calculus to find the time average of the velocity function.

5. Feb 26, 2008

### chocolatelover

Thank you very much

Regards