Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Find Velocity when Acceleration Vs Time Graph

  1. Jan 27, 2012 #1
    1. The problem statement, all variables and given/known data
    Find the particles Velocity at 7 seconds . ( Graph Below)


    2. Relevant equations

    3. The attempt at a solution

    T=5 from 7-2
    T=2 From 7-5 ( Because It's now -a)

    I tried int from 0 to 5 -10dt and got -50
    then AT=v with both
    A @ 7 second = (-20*2)/2 = -20

    Is velocity not negative.
    I am really embarrassed to ask for help. I would love to understand , and maybe remind me some how science is fun ..

    Attached Files:

  2. jcsd
  3. Jan 27, 2012 #2
    I will assume you are familiar with differentiation since it's listed under relavant equations. Do you know integration yet? If not, think about the graph of a constant acceleration - how do you find the velocity of a constant acceleration versus time graph?
  4. Jan 27, 2012 #3
    Yes , I am comfortable with doing integration.

    In this case I am not sure what is area. I know that area is from t 0 - 5 is on the positive side . I am not sure if I should add the two areas to find the v at 7s or something else.

    I haven't had I chance to talk about negative area to so it's just a bunch of assumitions , which I don't like.

    So , Should I find the area of the partial triangle then the other one below axis ?

    Or something else ?
  5. Jan 27, 2012 #4
    If I just do are both on the positive side and negative side of the a axis i get the quantities

    20 ( t , 1-2 ; up tri )
    20 (t 1-2 ; below rectangle )
    45 (t 2-5 ; large tri )
    20 ( t 5-7 ; tri in 4 quadrant ) ( is this positive or negative area )
    Last edited: Jan 27, 2012
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook