Colonel John P. Stapp, USAF, participated in studying whether a jet pilot could survive emergency ejection. On March 19, 1954, he rode a rocket-propelled sled that moved down a track at a speed of 632 mi/h. He and the sled were safely brought to rest in 1.40 s. (a) Determine the negative acceleration he experienced. (b) Determine the distance he traveled during this negative acceleration. Step 1 First, let's estimate the order of magnitude. We estimate the acceleration to be between 10g and 100g; that is, it is between roughly 100 m/s and 1000 m/s. We choose the straight track as the x axis and the direction of travel as positive. We expect the stopping distance to be on the order of 100 m. Step 2 We assume the acceleration is constant. We choose the initial and final times 1.40 s apart, bracketing the slowing-down process. We have a problem about motion under constant acceleration. With constant acceleration, we need to find the distance traveled during the 1.40 s time of the slowing-down process. Step 3 (a) Changing units of velocity vx in mi/h to m/s, we have the following conversion. 1609 m 1 h mi 3600 s Vxi = 632 mi/h m/s Now, we use the equation Vxf = Vxi + axt with xf = 0, and solve for ax. Vxf - Vxi t m/s m/s If the value of g is 10 m/s, this evaluates to approximately g.