Passage I

Students used 2 methods to calculate D, a car’s total stopping distance; D is the distance a car travels from the time a driver first reacts to an emergency until the car comes to a complete stop.

In Method 1, R is the distance a car travels during a driver’s assumed reaction time of 0.75 sec, and B is the average distance traveled once the brakes are applied. Method 2 assumes that D = initial speed in ft/secｘ2 sec. Table 1 lists R, B, and D for various initial speeds, where D was computed using both methods. Figure 1 contains graphs of D versus initial speed for Method 1 and Method 2.

Table 1 and Figure 1 adapted from Edwin F. Meyer III, Multiple-Car Pileups and the Two-Second Rule. ©1994 by The American Association of Physics Teachers.