Homework Help: Finding initial speed and accleration

1. Sep 2, 2007

hsma

1. A truck covers 50.0 m in 9.00 s while smoothly slowing down to final speed 2.40 m/s.

Find the trucks original speed.

Find its accleration.

2. Relevant equations
im using
x = v0*t + 1/2 *a*t2
and
v2 = v02 + 2*a*x

I believe this is what the question gives me.

Xo = 0
Xf = 50
Vo = ?
Vf = 2.4
a = ?
t = 9 secs

3. im positive that i have to use the two equations stated above. but both equations have accleration and Vo as unknown variables. i just need a hint on whats the best way to find accleration or Vo. I dont know if im clear what im saying but its the best way i can explain it. sorry.

2. Sep 2, 2007

bob1182006

Hm...ok I tried the problem (I suck @ sig figs hope you're better @ them).

$$x=x_0+v_0 t+\frac{1}{2}at^2$$
$$v=v_0+at$$

you could easily use the 2n'd formula to find a but you don't know initial v.

So use the first formula, since you're given begining/ending position and ending speed.
But you need to solve for initial v first. even though you don't know it you know that v=v0+at so move the variable's on the 2n'd formula to solve for initial v, plug that into the first and solve for a, and go from there.

3. Sep 2, 2007

hsma

thanks. worked them to get right answer. silly mistake using wrong equations.