Question

In order to qualify for the finals in an race, a runner must achieve an average speed of 5.24 m/s for the entire mile race. If she runs at a constant speed of 4.63 m/s for the first half of the 1609 meter race, what constant speed must she maintain for the second half of the race in order to qualify?

Answer 1

v=s/t=s/(t1+t2) = s/[(s/2•v1)+(s/2•v2)] =2•v1•v2/(v1+v2)
v2=v•v1/(2•v1-v)=5.24•4.63/(2•4.63-5.24) = 6.04 m/s