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Motion in Two Dimensions

  1. Jan 19, 2008 #1
    A small marble rolls horizontally with speed v0 off the top of a platform 2.75 m tall and feels no appreciable air resistance. On the level ground 2.00 m from the base of the platform, there is a gaping hole in the ground. The hole is 1.50 m wide. For what range of marble speeds v0 will the marble land in the hole.
     
    Last edited: Jan 19, 2008
  2. jcsd
  3. Jan 19, 2008 #2

    hage567

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    Maybe draw a diagram and label the information you know at certain points. What equations do you know that have to do with projectile motion? Explain where you are stuck with this problem. You must show some work, we won't do it for you.
     
  4. Jan 21, 2008 #3
    [​IMG]

    I'm thinking of finding the final velocity, or is that zero?
     
  5. Jan 22, 2008 #4

    Pyrrhus

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    Use the enery concepts (conservation law) in order to obtain the speed at the bottom, and then work it out from there.
     
  6. Jan 22, 2008 #5
    I haven't learned that yet. I'm supposed use the kinematics equations for this problem.
     
  7. Jan 22, 2008 #6

    Pyrrhus

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    You can still work it out. You know the marble must fall on 2.75 meters, so it can be inside the hole. Use v(0) as an unknown and work out the equations, probably since you know the distance, you could calculate the time it the marble takes and then find the value of v(0).
     
  8. Jan 22, 2008 #7
    This is what I calculated:

    Formula used: y(t) = y_0 + (v_0y)t + (1/2)(a_y)t^2
    0 = 2.75 + 0 - (1/2)(9.8)t^2
    t = 0.75s

    Then, I plugged time into the equation x(t) = x_0 + (v_0x)t
    2 = 0 + (v_0x)(0.7)
    v_0x = 2.86m/s

    I don't think my answers are reasonable though. Plus, I'm not sure of how to find v_0y.
     
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