Timing Worksheet for Stopping Distances

Timing Worksheet for Stopping Distances

1) Use a stopwatch and time vehicles from the prescribed starting point to the ending point.

2) Determine the cars’ speeds by dividing the distance travelled by the time.

(You may also calculate speeds using radar guns if they are available.)

3) Calculate your table’s average speed.

4) Use the data from your classmates to calculate your class’ average speed.

5) Safe stopping distance is calculated using the following equation:

d = V2 where d: deceleration distance in feet

2a V: vehicle speed in feet per second

a = 11.2 ft./sec.2 based on research

6) You must also account for the driver’s perception – reaction time to stop the vehicle.

The formula for the distance traveled during perception – reaction time is:

dr = V x t where V: vehicle speed in feet per second

t = 2.5 sec. based on research of time to perceive and react to the need to stop

7) The total distance traveled is the sum of distance traveled during braking (d) and during

perception – reaction time. The formula for the total stopping distance, SSD, is given by the following

formula:

SSD = d + dr where SSD = total stopping distance

d: distance traveled in braking in feet

dr : distance traveled during perception/reaction time in feet

Questions for Discussion

8) What factors could affect the speed of the cars on this section of the highway?

(Students could mention the fact the highway goes uphill, the fact they are coming to a stoplight,

weather conditions such as rain or snow, the amount of traffic at that time of day, etc.)

9) What factors could affect the driver’s perception-reaction time?

(Students could mention weather such as heavy rain or fog affecting vision, distractions such as

other passengers or texting while driving, intoxication, etc.)