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Where to start with this problem?

  1. Oct 20, 2013 #1
    1. The problem statement, all variables and given/known data

    You are pushing a 150-kg wooden crate in a straight line a distance of 4.5 m across a wooden floor at constant speed. The static and kinetic coefficients of friction are 0.42 and 0.30, respectively. What is the work done by you on the crate? and What is the work done by friction on the crate?

    I understand that with constant speed meas that my acceleration is zero, but after that I am lost.
    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 20, 2013 #2
    Show your work.
     
  4. Oct 21, 2013 #3
    ok here's what I did work is W=F*s.

    I multiply 0.30(kinetic energy) because the crate is in motion by 150kg by 9.81m/s^2 which gave me 441.45N as my frictional force. Now I have my force I will multiply it by my displacement to give me my work.

    441.45N*4.5m= 1986.525J.

    I did it and submitted the answer and received a 1/10 from this problem. What did I do wrong?
     
  5. Oct 22, 2013 #4
    Your solution seems fine for "work done by you". "work done by friction" would be negative of the calculated value. Also note that your answer should have only two significant figures. That means answer should have been ##2.0~kJ##. This could be the reason you were marked down.
     
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