Glider moving along an inclined track?

[sammyg18]

Homework Statement

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).

Homework 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.

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 :(

 

[HallsofIvy]

Using $v= v_0+ at$ and $x= v_0x+ (a/2)t$. With t= 8.2, x= 103.3 and v= 151, those become $151= v_0+ 8.2t$ and $(8.2^2/2)a+ 8.2v_0$. Solve those two equations for a and $v_0$.

 

[CWatters]

Duplicate thread..
https://www.physicsforums.com/threads/glider-moves-alone-an-inclined-track.811791/#post-5095751

 

[CWatters]

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.

Show your working for that.

I believe you made a sign error.