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The laws of motion - rock sliding on a roof

  1. Dec 22, 2013 #1
    The laws of motion -- rock sliding on a roof

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

    One side if the roof of a house slopes up at 37.0°.A roofer kicks a round,flat rock that has been thrown onto the roof by a neighborhood child.The rock slides straight up the incline with an initial speed of 15ms-1.The coefficient of kinetic friction between the rock and the roof is 0.400.The rock slides 10.0m up the rock and the roof crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof,with negligible air resistance.Determine the maximum height the rock reaches above the point where it was kicked.

    2. Relevant equations



    3. The attempt at a solution
    Are there anything wrong?
    Let the maximum height the rock reaches above the point where it was kicked be h.
    1/2mv2=mgh+fs
    1/2m(15)2=9.8mh+0.4xmx9.8xcos37°x10
     
    Last edited: Dec 22, 2013
  2. jcsd
  3. Dec 22, 2013 #2
    What is the acceleration the rock will undergo while sliding up the roof ? From this calculate the velocity of the rock just before it leaves the roof. What do you get ?

    Edit :You can also approach this problem using Work Energy concepts .
     
    Last edited: Dec 22, 2013
  4. Dec 22, 2013 #3

    SteamKing

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    Angles are not measured in degrees Celsius.
     
  5. Dec 22, 2013 #4

    haruspex

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    That looks right to me.
     
  6. Dec 22, 2013 #5

    TSny

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    Does the rock have any kinetic energy when it reaches maximum height?
     
  7. Dec 22, 2013 #6

    haruspex

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    Do I still get to keep my award for the year?:redface:
     
  8. Dec 22, 2013 #7

    TSny

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    :smile: (Definitely!)
     
  9. Dec 22, 2013 #8
    I think...no.
    This is because all the energy will convert to potential energy.
     
  10. Dec 22, 2013 #9

    TSny

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    What would happen to the rock (which is traveling along a parabolic arc) if it came to rest at its highest point?
     

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  11. Dec 23, 2013 #10
    Thanks!I can find the correct answer now!
     
    Last edited: Dec 23, 2013
  12. Dec 23, 2013 #11

    adjacent

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    :rofl:
     
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