How do I find missing terms in kinematic equations?

[cneedshelp]

An Olympic sprinter can accelerate from rest out of the blocks to a top speed of about 11.5 m/s. This is accomplished in the first 15 m of a race. What is the average acceleration of the first sprinter?
Given- vi- 11.5 m/s
Distance-15m
Vf-?
t-?
Which formula do I use to find these missing terms?

 

[tiny-tim]

hicneedshelp!

v_i = 0

v_f = 11.5

s = 15

and you want to find a …​

so which of the standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations do you think you should use?

 

[cneedshelp]

hicneedshelp!

v_i = 0

v_f = 11.5

s = 15

and you want to find a …​

so which of the standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations do you think you should use?

What is s?

 

[tiny-tim]

s is always distance

 

[cneedshelp]

s is always distance

Oh haha thank you. :)
Now how do you find the different times?

 

[tiny-tim]

what times??

(i don't see any times in the question )

 

[cneedshelp]

what times??

(i don't see any times in the question )

You have to find acceleration, the formula is vf-vi over tf-ti right?

 

[tiny-tim]

that formula certainly works if you know t

but you only know v_i v_f and s, and there is a formula using that information

 

[cneedshelp]

that formula certainly works if you know t

but you only know v_i v_f and s, and there is a formula using that information

d = vt + (1/2)at^2
is that the formula?

 

[tiny-tim]

d = vt + (1/2)at^2
is that the formula?

no of course not

 

[cneedshelp]

no of course not

Im not sure which formula to use...

 

[lightgrav]

what's their _average_ speed during that 15m ?
so how long should it have taken them to go 15m, at that average speed?

 

[tiny-tim]

(just got up :zzz: …)

Im not sure which formula to use...

there are three standard https://www.physicsforums.com/library.php?do=view_item&itemid=204" equations (click on the link)

you need to learn all of them