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Homework Help: Inclined plane and normal reaction force

  1. Sep 26, 2008 #1
    A block of mass M slides down a frictionless plane inclined at an angle è with the horizontal. The normal reaction force exerted by the plane on the block is

    a Mg.
    b Mg sin è.
    c Mg cos è.
    d zero, since the plane is frictionless


    2. Relevant equations

    Fn=mg cos è

    3. The attempt at a solution

    c

    is this right?

    thank you
     
  2. jcsd
  3. Sep 26, 2008 #2

    Redbelly98

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    Here is a simple way to check:

    What is the normal force when the angle is zero (horizontal surface)?
    What is the normal force when the angle is 90° (vertical surface)?

    Which choice is consistent with those two cases?
     
  4. Sep 26, 2008 #3
    9.8 is consistent. However, the book says, "unless angle = 0, Fn has magnitude less than the weight mg."
     
  5. Sep 26, 2008 #4

    Redbelly98

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    I don't understand your response.

    Are you sure the normal force is 9.8 when the face is vertical?

    And what do you mean "cos (0) = 9.8"??? The cosine of zero is 1.

    Your book is correct.

    Edit:
    You were also correct in your 1st post.
     
  6. Sep 26, 2008 #5
    thank you
     
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