How do I find missing terms in kinematic equations?

AI Thread Summary
To find the average acceleration of an Olympic sprinter who accelerates from rest to 11.5 m/s over 15 meters, the key kinematic equation to use is derived from the known variables: initial velocity (vi = 0), final velocity (vf = 11.5 m/s), and distance (s = 15 m). The discussion emphasizes that time is not directly provided, but can be calculated using the average speed during the distance covered. Participants suggest using the equation d = vt + (1/2)at^2, but clarify that it’s essential to know the correct formula to relate acceleration without time. Understanding and applying the standard kinematic equations is crucial for solving this problem effectively.
cneedshelp
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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?
 
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s is always distance :wink:
 
tiny-tim said:
s is always distance :wink:

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

(i don't see any times in the question :redface:)
 
tiny-tim said:
what times?? :confused:

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

You have to find acceleration, the formula is vf-vi over tf-ti right?
 
that formula certainly works if you know t

but you only know vi vf and s, and there is a formula using that information :wink:
 
tiny-tim said:
that formula certainly works if you know t

but you only know vi vf and s, and there is a formula using that information :wink:

d = vt + (1/2)at^2
is that the formula?
 
  • #10
cneedshelp said:
d = vt + (1/2)at^2
is that the formula?

no of course not :confused:
 
  • #11
tiny-tim said:
no of course not :confused:

Im not sure which formula to use...
 
  • #12
what's their _average_ speed during that 15m ?
so how long should it have taken them to go 15m, at that average speed?
 
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