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Homework Help: Am I doing this right?

  1. Oct 31, 2005 #1
    Hello

    I am I finding the derivative for this right??

    d = small delta

    s(t) = A Cos(wt + d)


    s'(t) = -A Sin(wt + d) * w

    s'(t) = -Aw Sin(wt + d)

    Is it correct to treat all the rest of the varibles as constants??? My text does not give any examples with these.

    All so what would make the velocity(s') = 0??

    Thanks

    Peter
     
  2. jcsd
  3. Oct 31, 2005 #2

    quasar987

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    Yep.


    Well you gotta ask yourself for what value(s) of t is s'(t) zero. To simplify the problem, make a change of variable y = wt + d. Find for what values of y is s'(y) zero, then find the corresponding values of t through t = (y-d)/w.
     
  4. Oct 31, 2005 #3
    Thanks.

    So if I am not given any values for w,d, or A would I just state that the velocity is 0 when wt + d = 0?
     
  5. Oct 31, 2005 #4

    TD

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    Is a sine only zero when the argument is zero?
     
  6. Oct 31, 2005 #5
    no it can be 0 at nPi. Is this correct???
     
  7. Oct 31, 2005 #6

    TD

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    Indeed, sin(x) is 0 when x is [itex]k\pi[/tex] with k an integer.
     
  8. Oct 31, 2005 #7
    thanks for your help
     
  9. Oct 31, 2005 #8

    TD

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    You're welcome :smile:
     
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