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Moving specular surface

  1. Nov 25, 2016 #1
    1. The problem statement, all variables and given/known data
    proxy.php?image=http%3A%2F%2Fimage.prntscr.com%2Fimage%2Ffa31e3ecf18e4bdab489b9cdb170fe63.png
    It's open container with water wich moves horizontally. It moves with some acceleration. Angle of incidence (α) and angle of reflection(β) on water are given (α=40 deg., β=20 deg.). We need to find container's acceleration.
    2. Relevant equations
    a=(v2-v1)/t (?)

    3. The attempt at a solution

    I've built angles of incidence and angles of reflection for both cases when v=0 and a=0 but what do to further is a big question for me (maybe this way of solution is wrong).

    I'll be grateful for the help
     
    Last edited: Nov 25, 2016
  2. jcsd
  3. Nov 25, 2016 #2

    haruspex

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    Is this your own diagram or was it provided?
    Have you stated the question, word for word, as it was given to you?
    I ask because it would be unusual for a horizontally accelerating body of water to have a horizontal surface.
     
  4. Nov 25, 2016 #3
    It's open container with water on car. Diagram was provided without vector a
     
  5. Nov 25, 2016 #4

    haruspex

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    Ok. Distrust the diagram.
    Consider a small parcel of water on the surface, or maybe some particle floating there, just submerged. Draw a free body diagram for it. What forces are there? How do these forces account for the acceleration?
    Alternatively, if you are comfortable with non-inertial frames, in the frame of reference of the car what are the forces?
     
  6. Nov 25, 2016 #5
    fa31e3ecf18e4bdab489b9cdb170fe63.png
    It's a copy of diagram and it moves horizontally
     
  7. Nov 25, 2016 #6

    haruspex

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    this diagram shows the container, not the water surface. Note that the incident and reflected rays are not shown meeting.
    In your original diagram you assumed acceleration was to the left.
     
  8. Nov 25, 2016 #7
    There is water inside that container. Yeah, and I can't understand why (how is it possible?).
    Acceleration to the left is my supposition
     
  9. Nov 25, 2016 #8

    haruspex

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    Yes, there is water inside, but the diagram does not show it, so you do not know what the surface looks like.
    Please try to answer my questions in post #4.
     
  10. Nov 25, 2016 #9
    6bf7b3cf048f4767bc244ad181cd9cbc.png
    Don't understand why I didn't see it
     
  11. Nov 25, 2016 #10

    haruspex

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    That looks much better.
     
  12. Nov 25, 2016 #11
    Thank you for help!
     
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