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Dynamic problem

  1. Oct 15, 2013 #1
    1. The problem statement, all variables and given/known data

    A student is skateboarding down a ramp that is 5.9 m long and inclined at 12° with respect to the horizontal. The initial speed of the skateboarder at the top of the ramp is 2.3 m/s. Neglect friction and find the speed at the bottom of the ramp.


    2. Relevant equations
    This is my steps:
    As I dont know the weight of the student, I dont know the force. So I cant use F-ma

    Vo=2.3
    Vox= 2.3cos78°= 0.48
    Voy= 2.3sin78°=2.25
    t=0.32


    ΔY (found by SOPHATOA) =Voy.t+1/2 a t^2
    1.23= 2.25t+1/2(9.8) t^2

    ΔX=Vox.t+1/2 a t^2
    5.8=0.48(0.32)+1/2.a.(0.32)
    ax=110.3

    Vx=Vox+at
    Vx=0.48+110.3(0.32)
    Vx=35.8

    Vy=Voy+at
    Vy=2.25+9.8(0.32)
    Vy=5.386

    therefore the resultant of Vx and Vy is 36.2

    3. The attempt at a solution

    my answer is wrong

    I really need some help :D
     
  2. jcsd
  3. Oct 15, 2013 #2
    Mg is counter-acted by normal force...
    For easier methods:
    You could just use conservation of energy.
    Or you could rotate the coordinate axes.(x-axis along the ramp, y perpendicular)
     
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