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: Sinusoidal functions

  1. Apr 16, 2009 #1
    1. The problem statement, all variables and given/known data

    The voltage, V(t), in volts, of a power supply can be modelled by the function V(t) = 110sin5t+15, where t is the time, in seconds. Find the maximum and minimum voltages, within the first second, and the times they occur.

    2. Relevant equations

    3. The attempt at a solution

    well, i think since the period is 5? that means there are 5 cycles, which means there will be 5 maximums, and 5 minimums, how do i figure out where the exact points are maximum?


    but how do i solve t there?
  2. jcsd
  3. Apr 16, 2009 #2


    User Avatar
    Gold Member

    You are correct to think that there will be 5 cycles. However, that is 5 cycles per 2[tex] \pi[/tex] radians. In order to find the zeros for your derivative, think about when does Cos(5t) = 0? It is equal to 0 whenever the argument inside cosine is [tex]\frac{\pi }{2} + n\pi [/tex]. Thus you can solve for [tex] 5t = \frac{\pi }{2} + n\pi \\ [/tex] with n = 0, 1, 2, 3.... but remember, only with t<1 second.
  4. Apr 16, 2009 #3
    What do you mean with "n"?
  5. Apr 16, 2009 #4


    User Avatar
    Gold Member

    n is an integer of 0,1,2,3.... etc etc. Remember, cosines and sines go on forever and they have an infinite number of zeros. The n tells you which zero you are at. For example, the n = 0 zero is at 5t = [tex]\frac{\pi }{2} [/tex]
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook