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Homework Help: Another physics problem that I do not know where to start!

  1. Nov 8, 2008 #1
    1. The problem statement, all variables and given/known data
    A small dutch boy, Hansel, and his little sister, gretal, were walking home from school along a polder when they saw a stream of water squirting horizontally fom a hole in the dyke. Hansel used a meter stick and found that the hole was a distance Y1= 1.05 m above the polder and that the water landed a distance X1= 1.51 meters from the base of the dyke. Hansel sent gretal running for help and stuck his finger, which had a cross sectional area A1= 1.00 cm^2 into the hole. While hansel waited for help, hansel established a crtesian coordinate system with +x in the direction of the stream and +y up with the origin at the polder.
    (A) Time, T, the water was in the air
    (B) the distance of the hole, Y2, below the surface of the north sea.
    (C) the velocity Vo,x of the water as it exits the hole
    (D) The velocity, V, of the water as it hits the polder
    (E) The cross sectional area, A, of the stream of water as it hits the polder
    2. Relevant equations
    the velocity and time equations need to be used

    3. The attempt at a solution

    I have been trying the past week to solve this problem and I do not know what equations I am suppose to use and how I am suppose to find them. I am completely lost on this problem and any help would be wonderful.
  2. jcsd
  3. Nov 8, 2008 #2

    Andrew Mason

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    The water starts moving horizontally. What causes it to fall to the ground (polder)? How far does it fall? How long does that take? You know the horizontal distance travelled in that time, so what is its horizontal speed?

    How is the horizontal speed of the water related to pressure at the hole and the area of the hole? How is the pressure related to the depth of the water at the hole?

    Answer those questions and you will solve each point.

  4. Nov 8, 2008 #3
    Gravity causes it to fall. It falls 1.05 meters. I do not know the time because that is what im trying to find. How do I find the horizontal speed? I also dont know how the speed is realted to the pressure and the area of the hole or the depth of the water at the hole.

    What are the equations I use to find the time, distance, velocity, and the cross sectional area??
  5. Nov 8, 2008 #4
    x = ut +(1/2)*at^2.

    Since the water stream is initially travelling horizontal (ie vertical component = 0)
    a = acceleration due to gravity
    x = 1.05 m. Solve for t.

    Also gravity is a force that only affects vertical motion - it has no effect on horizontal motion. So once you have the time, a simple velocity = distance/time calculation will give you the horizontal velocity, ignoring air resistance.
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