physics help!?

Question

a world class sprinter can burst out of the blocks to essentially top speed [about 11.5 m/s] in the first 15.0 m of the race. What is the average acceleration of the sprinter and how long does it take her to reach that speed?






=i dont get it help! :( i dont get the concept of velocity or accerleratation. : (

Answer 1

The average acceleration is change of velocity with respect to time:

a=(V2-V1)/(t2-t1)

also

S2=V1t2 + 0.5 a (t2)^2
V1=0 and t1=0
V2=11.5m/s; S2=15.0m

a=V2/t2

t2= sqrt(2 S2/a)
substituting t2 we have
a=V2/sqrt(2 S2 / a)
then
2 S2 a = V2^2 and
a= .5 V2^2/S2
a= 0.5 (11.5)^2 / 15=5.51m/s^2