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