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Homework Help: Acceleration using friction

  1. Mar 12, 2007 #1
    1. The problem statement, all variables and given/known data
    A person pushes horizontally with a force of 280 N on a 40 kg crate to move it across a level floor. The coefficient of kinetic friction is 0.30. the magnitude of the frictional force is 118.44. What is the magnitude of the crate's acceleration?



    2. Relevant equations
    Fn=ma
    fk=uk*Fn


    3. The attempt at a solution
    I figured out the first problem which was finding the magnitude of frictional force. I think I have to take 280N-118.44N for some reason. Thats just a gut feeling though.

    Im just not totally sure which equations to use and what order to use them

    Help would be great
     
  2. jcsd
  3. Mar 12, 2007 #2

    D H

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    Staff Emeritus
    Science Advisor

    Don't just guess. Draw a picture. In which directions are the two horizontal forces applied to the crate?
     
  4. Mar 12, 2007 #3
    ok, so the frictional force is countering the person's force. that would mean there is a 161.56N force still remaing pushing the box forward.

    How do get acceleration from this? a=Fn/m? so that would give me" a=(161.56)/(40). thus a=4.04. is this right?
     
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