Answer:
0.2583 m/s²
Step-by-step explanation:
The relationship between speed, distance, and time is ...
speed = distance/time
Of course, the relationship between the various units of measure is ...
- 1 km = 1000 m
- 1 min = 60 s
The average speed for the first 7.15 km was ...
(7150 m)/(1500 s) = 4 23/30 m/s
The acceleration is considered to be uniform over the 60-second period. The distance traveled during that time will be the same as the distance traveled at the initial speed for 30 s plus that traveled at the final speed for 30 s. That is, we can compute the final speed as though "Pre" ran 25.5 minutes (1530 s) at his initial speed and the remaining time (133.6 s) at his final speed.
The distance for 25.5 minutes at 4 23/30 m/s is ...
(1530 s)(143/30 m/s) = 7293 m
The remaining distance is then ...
10,000 -7,293 = 2,707 . . . meters
And the final speed is ...
(2707 m)/(133.6 s) ≈ 20.262 m/s
The acceleration is the change in speed divided by the time period:
(20.262 m/s -4.767 m/s)/(60 s) ≈ 0.2583 m/s²
_____
<em>Comment on these numbers</em>
According to this scenario, Pre's speed for the last 2000 meters, sustained for more than a minute, was more than 20 m/s -- about <em>double the world record</em> speed for a 100 meter sprint. It was a little more than <em>4 times</em> his speed for the first 25 minutes.
