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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

    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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