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Thread: Need help please

  1. #1
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    Need help please

    A ship is docked in port and rises and falls with the waves.
    The model h(t)=sin(PI/5)t describes the vertical movement of the ship, h, in metres at t seconds

    What is the period of the function?
    Determine all the times within the first minute that the vertical position of the ship is -0.9m to the nearest tenth of a second.


    I'm not sure as to how im supposed to figure these out. Am i supposed to actually draw the graph to represent this or something?
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  2. #2
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    Quote Originally Posted by sugar_babee
    A ship is docked in port and rises and falls with the waves.
    The model h(t)=sin(PI/5)t describes the vertical movement of the ship, h, in metres at t seconds

    What is the period of the function?
    Determine all the times within the first minute that the vertical position of the ship is -0.9m to the nearest tenth of a second.


    I'm not sure as to how im supposed to figure these out. Am i supposed to actually draw the graph to represent this or something?
    The period is $\displaystyle 2\pi$ divide by the frequency $\displaystyle \pi /5$ Thus,
    $\displaystyle \frac{2\pi}{1}\cdot \frac{5}{\pi }=10$

    For the second part you need to solve,
    $\displaystyle \sin(\pi /5 x)=-.9$
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  3. #3
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    How do i isolate the PI from the 5x? do i just multiply each side by it, or is there something more to it?
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  4. #4
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    Quote Originally Posted by sugar_babee
    How do i isolate the PI from the 5x? do i just multiply each side by it, or is there something more to it?
    No, you used take the inverse sine, thus,
    $\displaystyle \frac{\pi}{5}x=\sin^{-1}(-.9)$
    Thus,
    $\displaystyle x=\frac{5}{\pi}\sin^{-1}(-.9)$
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