# Velocity & acceleration

1. Oct 8, 2008

### physics_geek

velocity & acceleration!!

A truck covers 45.0 m in 8.00 s while smoothly slowing down to final speed 2.60 m/s.

a. the original speed?

b. the acceleration?

i have no idea how to do this
i thought i would use this formula

Vfinal = Vinitial + at.......but i need to know the acceleration which i do not know how to find

2. Oct 8, 2008

### LowlyPion

Re: velocity & acceleration!!

Perhaps you can find a more appropriate equation that takes into account the time and distance and velocity?
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

3. Oct 8, 2008

### physics_geek

Re: velocity & acceleration!!

well every equation i see..requires that you know the velocity and acceleration...which is what im trying to find

the only equation i think i can use is the average velocity...which would just be

45/8 = 5.625

i dont see how this helps

im totally lost

4. Oct 8, 2008

### LowlyPion

Re: velocity & acceleration!!

$$x = x_0 + v_0 t + (1/2) a t^2$$

5. Oct 8, 2008

### physics_geek

Re: velocity & acceleration!!

yea i was thinking abt that one

but wat would i put in for acceleration?!!?

6. Oct 8, 2008

### carltouss619

Re: velocity & acceleration!!

Why don't you try using this formula and this formula together.

In the first equation solve for Vo then plug that equation in the second equation. You see?

7. Oct 8, 2008

### LowlyPion

Re: velocity & acceleration!!

Actually you should consider solving the second one first for acceleration.
Then use the first to give you your final V.

8. Oct 8, 2008

### carltouss619

Re: velocity & acceleration!!

Yea but if you do it that way, you still don't know Vo ? That's why I said solve for Vo and then plug in because then everything else can be filled in accept for a. then that's how you get acceleration.

9. Oct 8, 2008

### LowlyPion

Re: velocity & acceleration!!

What if I said :
The a would be the same magnitude but different sign.

10. Oct 8, 2008

### carltouss619

Re: velocity & acceleration!!

Oh wow interesting never thought of it like that. true

11. Oct 8, 2008

### physics_geek

Re: velocity & acceleration!!

wow..i would never have figured that out

thanks a lot guys