Question

A 1500 m race is divided into 3 equal, 500 m, sections. In the first section, a racer accelerates from rest at 3.0 m/s^2. In section 2, his velocity reduces steadily to 70 m/s and in section 3, he constantly slows until he stops on the finish line. How long did the entire trip take?

Answer 1

stage I:
500 = 3/2 t^2
t = 18.26s
v = 3*18.26 = 54.78m/s

How can he "reduce" his speed from 54 to 70m/s in stage II?

What did I miss? Is there a typo?

Answer 2

the other equation you can use use is:
Vf^2=Vi^2+2AX
sqrt(2(3m/s^2)(500m))=54.78 m/s

same thing.

for the second part you use the same equation and solve for A. Then plug it in to Vf=Vi+AT, solve for T.

for the third you do the same thing.