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

Homework Help: 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)

    attachment.php?attachmentid=43187&stc=1&d=1327701197.jpg


    2. Relevant equations
    attachment.php?attachmentid=43188&stc=1&d=1327701250.jpg




    3. The attempt at a solution

    T=5 from 7-2
    or
    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