A runner runs a 10 metre race, the runner runs according to the following rule:

s = 0.2t(t - 5.1)(t - 9.1)
Where displacement (s) is in metres and time (t) is in minutes.

Calculate for the runner:
their starting position
any changes in direction over the race (when and where it happened)
their finishing time for the race

1 answer

s(0) = 0

a little calculus (or inspection of the graph) will show that the runner changed direction at t=2.1 and t=7.4

s=10 when t≈10

http://www.wolframalpha.com/input/?i=plot+y%3D0.2t%28t+-+5.1%29%28t+-+9.1%29%2C+y%3D10