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Sliding Block on Incline

  1. Oct 15, 2008 #1
    1. The problem statement, all variables and given/known data

    A 5.0 kg block slides along a frictionless horizontal surface with a speed of 7.0 m/s. After sliding a distance of 3.0 m, the block makes a smooth transition to a frictionless ramp inclined at an angle of 40° to the horizontal. How far up the ramp does the block slide before coming momentarily to rest?
    m


    2. Relevant equations

    F=ma
    v^2=v(initial)^2+2ad

    3. The attempt at a solution

    v(initial)=7.0 m/s
    F(net)=Fn-Fg; Fn-Fg=ma
    Fn=5*9.81*cos 40
    Fg=5*9.81
    F(net)=-11.4755
    a=F(net)/m
    a=-2.2951

    0=v(initial)^2+2ad
    0=7^2+2(-2.2951)d
    0=49-4.5902d
    d=49/4.5902
    d=10.67

    I tried this but it was incorrect. I think I might need to account for the 3 meters before the incline in order to find the initial velocity but since the surface was frictionless and there was no given acceleration is there a change in velocity during that time?
     

    Attached Files:

  2. jcsd
  3. Oct 15, 2008 #2

    Hootenanny

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    You might want to reconsider the net force acting on the block when it is on the incline.
     
  4. Oct 15, 2008 #3
    Since it is a frictionless surface I didn't think there were any forces other than normal and gravity?
     
  5. Oct 15, 2008 #4

    Hootenanny

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    You're correct, the only two forces are the normal force and the weight of the mass. However, what is the net force acting on the mass? In which direction does it act?
     
  6. Oct 15, 2008 #5
    Oh okay so it was sin instead of cos thank you very much!
     
  7. Oct 15, 2008 #6

    Hootenanny

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    No, what I'm saying is that the normal force has nothing to do with it! The only net force acting on the mass is the component of gravity which acts parallel to the slope, the normal force is irrelevant.
     
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