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Newton Law problems

  1. Nov 11, 2006 #1
    An applied force of 50 N is used to accelerate an object to the right across a frictional surface. The object encounters 10 N of friction. Use the diagram to determine the normal force, the net force, the mass, and the acceleration of the object. (Neglect air resistance.)
    this is the image she gave us: http://faculty.xavierhs.org/wertkins/ipcf1113_files/image001.gif

    The picture is what is throwing me off, i thought the normal force would be what the object was actually moving at so 50n-10n= 40n. But i dont know what a net force is. I think the force of the object downward is how much it weighs so (w=m*g) 80=m*10 m=8 kg. Also to find the acceleration i dun know to use the normal force or net force in A=f/m
     
  2. jcsd
  3. Nov 11, 2006 #2
    Double check your definitions. The net force is the sum of all ther forces on the object. The normal force is between the object and the surface.

    I think your instructor is trying to teach you to the basics of drawing and using free-body diagrams.... you might want to look up so websites on that technique, or maybe there's a good tutorial on this site.
     
  4. Nov 11, 2006 #3

    radou

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    Also, note that the direction of the net force is the same as the direction of the acceleration.
     
  5. Nov 11, 2006 #4
    The object will move according to F=ma, where F is the sum of all the forces acting on it, m=8kg as you've already found, and a is an acceleration of the object, which is in the direction of F.
     
  6. Nov 11, 2006 #5
    The normal force is the same as the gravitational force, so Fnorm= 80N. Then I found out the mass by using the formula M=w/gàM=80n/10, the mass is 8kg. Then to find the net force you just do 50n (Fapp) – 10 N (Ffric) and you find out the net force is 40N. Then with this I was able to find the acceleration by using A=f/màA=40n/8, the acceleration is 5 m/s2.
     
  7. Nov 11, 2006 #6
    is that right?
     
  8. Nov 11, 2006 #7

    radou

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    Yes, looks correct.
     
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