North Carolina RADAR State Practice Exam

What is the total stopping distance at a speed of 20 MPH?

1. 62 ft

2. 42 ft

3. 34 ft

4. 22 ft

The correct answer is: 42 ft

To determine the total stopping distance at a speed of 20 MPH, it's essential to understand that total stopping distance is comprised of two key components: the perception/reaction distance and the braking distance. 1. **Perception/Reaction Distance**: This is the distance a vehicle travels while the driver is recognizing the need to stop and reacting to it. At 20 MPH, a driver generally has a perception/reaction time of about 1.5 seconds. To calculate this distance, you can use the formula: (speed in feet per second) x (reaction time). At 20 MPH, the speed in feet per second is approximately 29.33 feet (since 20 mph is about 29.33 feet/second). Thus, the perception/reaction distance is around 29.33 ft x 1.5 seconds, which equals approximately 44 ft. 2. **Braking Distance**: This is the distance a vehicle travels from the point where the brakes are applied until it comes to a complete stop. The braking distance can vary based on factors such as road conditions and the vehicle's braking efficiency. A general rule is that stopping distance increases with the square of the speed. For a vehicle traveling at 20 MPH,