1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Velocity vs.Time graph

  1. Aug 4, 2008 #1
    I have question about the velocity vs. time graph about a slope that is below the x-axis. I was doing a problem about this:

    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. jcsd
  3. Aug 4, 2008 #2


    User Avatar
    Science Advisor

    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?
  4. Aug 4, 2008 #3


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook