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!

Homework Help: Net Change Theorem help

  1. Jan 16, 2010 #1
    1. The problem statement, all variables and given/known data
    http://img39.imageshack.us/img39/8019/92452636.jpg [Broken]


    2. Relevant equations



    3. The attempt at a solution
    i got -234 for the last part but it should be abs.value so 234.. but it didnt work.
    is my work correct?
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jan 16, 2010 #2

    Mark44

    Staff: Mentor

    No. You have v(t) = (t - 8)(t + 3), which is correct, but it's not true that v(t) <= 0 on the interval [6, 11]. Where did the 11 come from? Think about what the factors of v(t) mean. v(t) = 0 only for t = -3 and t = 8. These two numbers divide the number line into three regions, on two of which v(t) > 0 and on one of which v(t) < 0.
     
  4. Jan 16, 2010 #3
    v(t) > 0 on [-infinity,-3] and [8, infinity]
    v(t) < 0 on [-3, 8]

    so how do i express the antiderivative?
     
  5. Jan 16, 2010 #4

    Mark44

    Staff: Mentor

    [tex]\int_6^{12} |v(t)|dt~=~\int_6^8 -v(t) dt~+~\int_8^{12} v(t) dt[/tex]

    Isn't that what you're trying to do?
     
  6. Jan 16, 2010 #5
    that what i didnt understand how to set up..
    so pretty much you take the number you got for t (which was t= -3, 8)
    you pick the one that in the interval [6, 12] (in this case, 8)
    and then make it 6 -- > 8 + 8 --> 12
    i got it. sweet tnx a lot!
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook