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How much work and how much force do we use in pushing a box

  1. Oct 22, 2009 #1
    1. The problem statement, all variables and given/known data

    How much work do we do when we pull a wooden block with a mass m = 1 kg and we displace it for ∆x= 1 m. The object is being pulled on a rough surface with a coefficient of friction µ_k = 0.1. We are pulling the object with a string; the angle between the string and the surface is 30º. How much strength are we using when pulling the wooden block if the block is moving at 1 m/s at all times.

    2. Relevant equations

    F_k= µ_kN
    F=ma
    N= mg-Fsinθ
    W= F∆x

    3. The attempt at a solution

    1) How much work is done:

    F_k= µ_kN → F_k= µ_kmg= 0.98N
    W= F∆x= 0.98J

    2) How much strenght are we using:

    W= F∆xcosθ
    F= W/ ∆xcosθ= 1.12N
     
  2. jcsd
  3. Oct 22, 2009 #2

    Delphi51

    User Avatar
    Homework Helper

    Those look good. You might check 2 again - for .98/cos(30) I get 1.13 instead of 1.12.
     
  4. Oct 22, 2009 #3
    Yes, you are right, it is 1.13 N.

    Thank you for your help! Have a nice day!
     
    Last edited: Oct 23, 2009
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