# 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).

first your formula's are wrongish:

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

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.