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Inclined plane problem, weight of subject

  1. Apr 2, 2009 #1
    1. The problem statement, all variables and given/known data


    This man has mass 'm' and the angle of the plane is 'x'. The inclined plane is frictionless. He is standing on a scale which is placed on top of the blue wedge, what weight will the scale measure?

    2. Relevant equations


    3. The attempt at a solution

    If the man was standing on a regular block, I would say his weight would be equal to


    But I am confused as to whether standing on a wedge would change things.

    Thanks for trying to help!
  2. jcsd
  3. Apr 2, 2009 #2


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    The block is sliding with an acceleration gsin(theta). Find its vertical component. When the block is falling freely, the reaction or reading in scale will be zero. If it is falling vertically with some acceleration, what will be the reaction?
  4. Apr 2, 2009 #3
    Well, if the man was on a block like the following:


    And that ramp was inclined at angle theta, I would say that the downwards acceleration would be gcos(theta), and so the scale would read mgcos(theta).

    But, in the problem from the first post with the blue wedge, the man and the scale are actually standing on a flat surface.

    So, in that case, I don't know how to draw the vectors in order to figure out what force is being put on the scale.
  5. Apr 2, 2009 #4


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    In the first case if the block is stationary, the scale will read his weight. Since it is sliding, the new weight will be m(g-a). In non inertial frame, pseudo force is in the opposite direction to the actual force.
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