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Homework Help: Velocity-Time Graphs and Friction

  1. Sep 11, 2012 #1
    1. The problem statement, all variables and given/known data
    An object moves up and down an inclined, frictionless surface.
    1) Draw a Velocity-Time Graph of this situation.
    2) If there was friction, how would it impact the graph?

    2. Relevant equations
    Ek = 1/2 m v^2
    Eg = mgh
    Ek = Eg
    I don't think the equations are necessary in the solution, but I included these equations since energy must be conserved as the object moves on the surface, so the final and initial speeds must be the same too.

    3. The attempt at a solution
    Since the track is frictionless, acceleration should be constant. This means that the velocity graph should be linear with a constant slope. If friction is involved, it will oppose the direction of motion meaning the acceleration up the incline and down the incline will be different, meaning that friction works the same no matter if the object is moving upwards or downwards. So, the velocity graph will not be linear in shape. When the object moves downwards, it should speed up because the parallel component of the gravitational force is in that direction. In that case, the graph should look like a V. Is this correct?
  2. jcsd
  3. Sep 11, 2012 #2
    The magnitude of acceleration is constant in the first case, not the direction. If the body moves up again, the motion retards instead of getting accelerated.
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