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Basic Mechanics Question!

  1. May 20, 2009 #1
    My exam is in an hour, so quick replies are dearly needed!

    http://www.ph.qmul.ac.uk/phy116/Exams/Mid%20Term%20Test%202006%20Answers.pdf [Broken]
    Question 3)a

    I would have said the force exerted by the RAMP on the MASS is mgcos30, not mg as my lecturer has said (and it's the same in every paper).

    What am I not seeing here? The only thing I can think of is due to the axis of where F is.

    Thanks!
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 20, 2009 #2

    diazona

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    The block is not moving, thus a = 0. Also, gravity pulls down on the block with a force equal to mg. If you accept these two facts, balance the forces in the vertical direction and see what you get.
     
  4. May 21, 2009 #3

    Redbelly98

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    I just saw this post, too late for the exam, but I have a comment that may help.

    mg cos30 is the normal force exerted by the ramp on the block. But the question is really asking for the total force F exerted by the ramp, which includes the friction and normal forces.

    As diazona said, F must balance against the downward, vertical force mg.
     
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