# 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 formulahttps://www.physicsforums.com/latex_images/90/905663-3.png [Broken] and this formula https://www.physicsforums.com/latex_images/90/905663-4.png [Broken] together.

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

Last edited by a moderator: May 3, 2017
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.

Last edited by a moderator: May 3, 2017
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