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Homework Help: Kinematics Water shooting out of hose

  1. May 22, 2010 #1
    1. The problem statement, all variables and given/known data

    Suppose you adjust your garden hose nozzle for a hard stream of water. You point the nozzle vertically upward at a height of 1.5 above the ground. When you quickly turn off the nozzle, you hear the water striking the ground next to you for another 2.0 . find the water speed as it leaves the hose nozzel


    2. Relevant equations

    v = v_o + at
    x = x_o + v_o*t + (1/2)at^2
    v^2 = v_o^2 + 2a(x - x_o)
    v_a = (v + v_o)/2

    where v_o is initial velocity x_o is initial distance v_a is average velocity

    3. The attempt at a solution

    dunno if I can actually do this but I derived my own equation adding the top half (the parabola area) and the bottom the part equal 1.5m


    0 = 2v_o + 19.6t ( v_o + at) for both 2 halfs of the parabola


    -1.5 = v_o*t + 4.9t^2

    add top and bottom

    0 = v_o*t - 4.9t^2 +1.5 + 2v_o + 19.6t


    -v_o = (-4.9t^2 + 19.6t +1.5)/ (t+2)

    solve for v_o with t = 2

    v_o = 5.275 m/s

    I dunno if I was mathematically correct to add those equations together, can anyone help please

    Thank You.
  2. jcsd
  3. May 22, 2010 #2
    Sorry hanlon but your work is hard to follow. Use the subscript and superscript buttons provided above the input text field when posting, and any other necessary formatting to make it easier to read. You've also written down equations with values already plugged in without specifying which of the relevant equations you've used. It's hard to see where those values came from.

    Where does the value 19.6 come from? Also, can you tell me how you got those equations you're using? Are they derived from the relevant, constant acceleration equations?
    Last edited: May 22, 2010
  4. May 22, 2010 #3


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    Staff Emeritus
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    Homework Helper

    I, too, did not follow your derivation. Let's look at those equations again:
    Let's make a list of all the quantities that appear here:
    (Since va is simply (x-x0)/t, I didn't bother listing it.)
    Question for you: which of the quantities are given in the problem statement? Which quantity is being asked for? That information should help with choosing which equation (in your list above) will work out for this problem.
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