# Velocity vs.Time graph

1. Aug 4, 2008

### Gear2d

I have the x-axis as my time and y-axis as my velocity. Now at 3 seconds where velocity is -30 m/s to 6 seconds where velocity is 0 m/s, is acceleration "+" because it is in the same direction as velocity (since velocity is getting more positive and positive, -30, -25, -15,...)?

2. Aug 4, 2008

### uart

Becuase t=6 seconds occurs later than t=3 seconds you should use v(3)=-30 as the *initial* velocity and v(6)=0 as the *final* velocity. Correct that and then you'll get the correct answer. Makes sense right?

3. Aug 4, 2008

### Hootenanny

Staff Emeritus
Acceleration can be defined as the time derivative of velocity, which is the gradient on the velocity - time curve. So yes, if the gradient of the curve is positive (i.e. velocity is increasing) then the acceleration is positive.