Final answer:
The athlete's average speed for the entire 5-km race would be less than 8 km/h because the time taken to tie their shoe adds to the overall time, lowering the average speed since average speed is calculated using total distance divided by total time, including any stops.
Step-by-step explanation:
An athlete running a 5-km race at an average speed of 8 km/h would have an average speed less than 8 km/h for the entire race if they stopped to tie their shoe because average speed is calculated by dividing the total distance traveled by the total time taken. The time spent tying the shoe adds to the total time without adding to the distance covered, which in turn decreases the overall average speed.
For example, if the runner initially expected to complete the race in 37.5 minutes without interruption, any additional time spent not running, such as tying their shoe, would extend the overall time taken to complete the race. Assuming the shoe-tying took 1 minute, the race would then be completed in 38.5 minutes, and when we calculate the new average speed, it would be the total distance (5 km) divided by total time (38.5 minutes converted to hours, which is approximately 0.642 hours), resulting in an average speed of about 7.79 km/h, slightly less than 8 km/h.
It's similar to a car trip where if you travel a certain distance at a constant speed but then stop for gas or rest, your average speed for the trip would be less than your driving speed due to the stops.