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Homework Help: Find the normal force and magnitude of acceleration.

  1. Sep 20, 2009 #1
    1. The problem statement, all variables and given/known data

    A horizontal force of 100 N pushes a 12-kg block up a frictionless incline that makes an angle of 25° with the horizontal. (Use g = 9.81 m/s2.)
    1. What is the normal force, in Newtons, that the incline exerts on the block? Round your answer to two significant figures.

    2. What is the magnitude of the acceleration of the block in m/s2? Round your answer to one decimal place.

    2. Relevant equations



    3. The attempt at a solution

    1. I got it as 117.72. Is it right? And if it's right how do I round to 2 significant figures.
    2. I don't know how to find acceleration.
  2. jcsd
  3. Sep 20, 2009 #2
    For the first one, remember that the normal always make a 90 degree angle with the surface. So your first result is not correct.

    The second question is best solved using the normal force, the horizontal force, some trigonometry and Pythagoras. Try to solve the first one, and then you can get further help with the second question.
  4. Sep 20, 2009 #3
    What I did is F=ma => F=12*9.81m/s^2
    How do I substitute 90 degree in that?
  5. Sep 20, 2009 #4

    Know that gravity works strait down and figure out the angle a, then use appropriate trigonometric functions to calculate the answer. The non-strait-down line in the sketch is the normal.
  6. Sep 20, 2009 #5
    I got the acceleration as 56.9 m/s^2 Is it right?
    But I still can't find what's normal force.
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