Question

A runner approaches the finish line and is 75m away; her average speed at this position is 8m/s. She decelerates at this point at 0.5 m/s2. How long does it take her to cross the finish line from 75cm away?

Answer 1

The distance
s=v_0 t+(at^2)/2
So
75=8t-0.25t^2
Or
0.25t^2-8t+75=0
Root
t=40 s