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Glider moving along an inclined track?

  1. May 2, 2015 #1
    1. The problem statement, all variables and given/known data
    In a classroom demonstration, a glider moves along an inclined track with constant acceleration. It is projected from the low end of the track with an initial velocity. After 8.2 s have elapsed, it is 103.3 cm from the low end and is moving along the track at a velocity of -15.1 cm/s. Find the initial velocity (cm/s) and the acceleration (cm/s^2).

    2. Relevant equations
    xf = xi + 0.5 (vi + vf) t
    xf = xi + vi t + 0.5 a t^2
    a = (vf - vi)/t

    I honestly might be using equations that are totally wrong. I have no idea.

    3. The attempt at a solution
    First I tried xf = xi + 0.5 (vi + vf) t and I came up with 10.1 cm/s for vi but that's wrong. Then I tried xf = xi + vi t + 0.5 a t^2 and I plugged a = (vf - vi)/t Into the equation for a but I couldn't solve it through for vi. I'm definitely missing something or doing something wrong :(
     
  2. jcsd
  3. May 2, 2015 #2

    HallsofIvy

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    Using [itex]v= v_0+ at[/itex] and [itex]x= v_0x+ (a/2)t[/itex]. With t= 8.2, x= 103.3 and v= 151, those become [itex]151= v_0+ 8.2t[/itex] and [itex](8.2^2/2)a+ 8.2v_0[/itex]. Solve those two equations for a and [itex]v_0[/itex].
     
  4. May 3, 2015 #3

    CWatters

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  5. May 3, 2015 #4

    CWatters

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    Show your working for that.

    I believe you made a sign error.
     
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