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Homework Help: Determining the static and kinetic coefficients on an incline of wood on wood!

  1. Oct 21, 2008 #1
    1. The problem statement, all variables and given/known data

    This was a lab task in which we are asked: Determine the static and dynamic coefficients of friction for a block of wood of mass 82.2grams on a plank of wood.

    PART A:
    To determine the static coefficient we found the angle at which point the block just started to move. This was 45.4 degrees.

    For Part A, I used the equation fr = tan 45.5 degrees which gave me an answer of 1. I am not sure if this is to be expected static coefficient of a polished block of wood on a plank of wood as anything else I have read has always had a lower coefficient.

    PART B:
    To determine the kinetic coefficient we increased the angle to 50 degrees and timed how long the block took to cover the plank, a distance of 1 meter, when released from the top. The average time was found to be 0.69s. This is where I get stuck! I do not know how to calculate the kinetic coefficient and after much research on the net I am still as stuck as I first was... The block is accelerating but I don't know how to determine the acceleration or whether that is even necessary. Furthermore, can I just state the velocity is 0.69ms-1?
    Can someone please just suggest a starting point...
  2. jcsd
  3. Oct 21, 2008 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Try the kinematic equations, they're the ones that relate time, distance, velocity and acceleration when the acceleration is constant.
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