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Homework Help: Conceptual Questions Fluids and Simple Harmonic motion

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

    1. Do you use the equation of continuity and Bernoulli's equation simultaneously in a question? When do you use them?

    2. In simple harmonic motion, why is the velocity shifted to left of the displacement by pi/4?

    2. Relevant equations

    pressure + .5density x velocity ^2 + density x g x y (initial)= the same thing (final)

    A1V1=A2V2 (continuity)

    x(t)=xmaxcos(wt + phi) here w=omega

    3. The attempt at a solution

    I've been reading my book, but I am confused about these issues. Please help.
  2. jcsd
  3. Apr 16, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    In all sorts of problems involving streamlined fluid flow. For example, flow through a pipe of varying height and cross-sectional area.

    I think you mean pi/2. To see this, imagine a ball on a spring oscillating back and forth along the x axis. When it passes through the equilibrium point (going towards +x, say) its speed is at its maximum positive value while the displacement is at zero. When it gets to maximum displacement, the speed now is zero. When it returns to equilibrium, its displacement is again zero, but the speed is maximum negative. And so on. Sketch out the diagrams of displacement and velocity (both sinusoids) and you'll see that the velocity graph looks exactly like the displacement graph, just slid over to the left by pi/2.
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