Final answer:
The student's speed decreased by 5 m/s.
Step-by-step explanation:
To calculate the decrease in speed, we need to find the difference between the initial speed and the speed after running 300 m in 30 seconds.
First, let's find the initial speed using the information from problem 7. The initial speed is calculated by dividing the distance (300 m) by the time (20 seconds). So, the initial speed is 300 m/20 s = 15 m/s.
Now, let's find the speed after running 300 m in 30 seconds. The speed is calculated by dividing the distance (300 m) by the time (30 seconds). So, the speed after running 300 m is 300 m/30 s = 10 m/s.
To find the decrease in speed, we subtract the speed after running 300 m from the initial speed: 15 m/s - 10 m/s = 5 m/s.