How Do You Calculate Initial Speed and Acceleration of a Slowing Truck?

[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

 

[LowlyPion]

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

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

 

[physics_geek]

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

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

45/8 = 5.625

i don't see how this helps

im totally lost

 

[LowlyPion]

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

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

45/8 = 5.625

i don't see how this helps

im totally lost

Well what about this one?

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

 

[physics_geek]

yea i was thinking abt that one

but wat would i put in for acceleration?!?

 

[carltouss619]

Why don't you try using this formulahttps://www.physicsforums.com/latex_images/90/905663-3.png and this formula https://www.physicsforums.com/latex_images/90/905663-4.png together.

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

 

[LowlyPion]

Why don't you try using this formulahttps://www.physicsforums.com/latex_images/90/905663-3.png and this formula https://www.physicsforums.com/latex_images/90/905663-4.png together.

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

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

 

[carltouss619]

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

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.

 

[LowlyPion]

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.

What if I said :

A truck covers 45.0 m in 8.00 s while smoothly speeding up from an initial speed of 2.60 m/s.

The a would be the same magnitude but different sign.

 

[carltouss619]

What if I said :


The a would be the same magnitude but different sign.

Oh wow interesting never thought of it like that. true

 

[physics_geek]

wow..i would never have figured that out

thanks a lot guys