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Homework Help: Drawing a free-body diagram?

  1. Mar 18, 2014 #1
    1. The problem statement, all variables and given/known data

    A person pushes perpendicularly on a block of wood that has been placed against a
    wall. Draw a free body diagram and identify the reaction forces to all
    the forces on the block.

    2. The attempt at a solution


    I'm not exactly sure if I've covered all the forces or if I'm looking at this the wrong way. I was also thinking gravitational force should be included?
  2. jcsd
  3. Mar 18, 2014 #2
    The free body diagram is not correct. Mainly the directions of the forces that you included are wrong.

    You are right in that you should include gravity and you should assume the block is in equilibrium i.e. it's not moving.
  4. Mar 19, 2014 #3
    I don't understand why my directions are wrong. Wouldn't the forces of the the box being pushed and the force between the wall and the box go to the right while the frictional force acts on the opposite direction and go to the left?
  5. Mar 19, 2014 #4


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    Is the wall on the right side? If so then consider the normal force exerted by the wall: is it pulling the box toward the wall or pushing it away?
  6. Mar 19, 2014 #5
    It just said it was moving perpendicularly against the wall. The normal force between the box and the wall would be the wall exerting force towards the wall, right, and then the wall would be exerting the same force to the box, left. Am I looking at the wrong way?
  7. Mar 19, 2014 #6


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    I assume you meant box?

    So if the wall is exerting the normal force on the box, to the left, why does your diagram show this force pointing to the right?
  8. Mar 19, 2014 #7
    Our professor told us to treat it as a force directly going to the right of the diagram.
  9. Mar 19, 2014 #8
    The convention is usually to draw the force on the side that it is acting. So if the wall is located on the left side of the block you should draw the corresponding force on that side.
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