Science students used 2 different methods to calculate the total stopping distance of a vehicle (Z). Z is the total distance a vehicle travels from the time the driver first reacts to the emergency all the way until the car comes to a complete stop. 

In Method 1, X is the distance a car travels during the driver's assumed reaction time of 0.75 

Method 2 simply assumes that Z is the initi speed in feet per second times 2 seconds. (Z = speed x 2). Table 1 shows X, Y, and Z for seve different initial speeds, where Z is calculated using both methods. Figure 1 is a graph of Z initial speed for Methods 1 and 2.