1. The problem statement, all variables and given/known data in a women's 100-m race, accelerating uniformly, Laura takes 2.00 s and Healan 3.00 s to attain their maximum speeds, which they each maintain for the rest of the race. They cross the finish line simultaneously, both setting a world record of 10.4 s. What is the acceleration of each sprinter? 2. Relevant equations vf = vi + at xf = xi + .5(vi + vf)t xf = xi + vit + .5at^2 vf^2 = vi^2 + 2a(xf-xi) where vf, vi, xf and xi are final and initial velocity and horizontal position (respectively) 3. The attempt at a solution xf = xi + vit + .5at^2 100 = (0) + vit + .5a(10.4)^2 9.62 = vi + 5.4a avg velocity = 100/10.4 = 9.61 m/s a = v/t a (Laura) = 9.61 / 2 = 4.8 m/s^2 a (Healan) = 9.61 / 3 = 3.2 m/s^2 my books answers are 5.32 m/s^2 for laura and 3.75 m/s^2 for healan. i don't know how to get there... I've tried using all of the above equations, but I can't get anything to work out because I have too many unknowns (vf, vi, and a). For awhile I tried using 0 as the value of vi and xi, but that didn't work out, either. I can't figure out how to use the information about the time each person reached maximum speed (or if it should be used at all).