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Work, friction and gravety

  1. Feb 19, 2014 #1
    Work, friction and gravity

    1. The problem statement, all variables and given/known data

    pic.png
    Calculate the work done on the slanted portion by gravity and friction


    2. Relevant equations

    3. The attempt at a solution

    Work is Fdx

    F:
    Gravity is [itex]L\sin\left(\theta\right)mg[/itex]
    Friction is [itex]L\cos\left(\theta\right)mg\mu_{1}[/itex]

    dx:
    Friction travels along a path L, but is this also true for gravity?

    Simply squaring the L's and adding them together, or subtracting friction, registers as incorrect.
     
    Last edited: Feb 19, 2014
  2. jcsd
  3. Feb 19, 2014 #2
    You already calculated the work done by gravity and friction. as you said
    Gravity is Lsin(θ)mg
    Friction is Lcos(θ)mgμ1

    Friction doesn't travel, friction is a phenomenon caused by gravity, gravity always acts "straight down". The vector of the force of friction is parallel to the ramp's surface, yes. mg sin(a) is the ramp directional component of the force of gravity (imagine it as an invisible rope being pulled by invisible somebody).

    assuming L is the distance the block travels down the ramp, then the above are the work done by the respective forces.

    If you wanted to find out the total energy spent in this process, then you would have to add them together, don't create energy out of nothing, though.
     
  4. Feb 19, 2014 #3
    Not sure why I rambled about squaring the L's.
    There was a problem with the website, I hate those digital things.
    Thanks anyway.
     
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