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Where brick hits ground after sliding off a roof w/ friction

  1. Dec 19, 2015 #1
    1. The problem statement, all variables and given/known data
    Brick is sliding off a roof, starts at the peak of the roof (7.0 m above ground), slides down roof with kinetic friction value of 0.28, very edge of roof is 4.0 m above ground. Where does the brick land on the ground?
    Please see image - http://imgur.com/wNdtlWD

    2. Relevant equations


    3. The attempt at a solution
    I attempted the solution by:

    drawing force diagram of brick (@ = angle of incline, 30 degrees) which gives the acceleration down (acceleration down the roof = positive direction) the roof by:
    ma = mgsin@ - frictional force
    ma = mgsin30 - 0.28

    Now should I just continue to solve for the acceleration and then treat this as a projectile? If so, can someone walk me through it?


    Thanks!
     
  2. jcsd
  3. Dec 19, 2015 #2

    haruspex

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    0.28 is not the frictional force. It is the coefficient of kinetic friction. How do you obtain the frictional force from the coefficient?
     
  4. Dec 20, 2015 #3
    Oh yeah!
    The frictional force (Ff) = coefficient of kinetic friciton * Fn = 0.28 * mgcos@
     
  5. Dec 20, 2015 #4

    haruspex

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    Good.
    So, at what speed does it leave the roof?
     
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