D A marathon runner runs at a average speed of 5.33 meters per second for the first

73600 seconds and then at a speed of 5.00 meters per second for the next 4200

seconds. What is the average speed of the marathon runner in meters per second?

F

5.1 m/s

G

2.6 m/s

H

0.4 m/s

J 1.06 m/s

The average speed of the marathon runner is 5.15 meters per second

Explanation:

Lets revise the meaning of average speed

The average speed of an object is the total distance traveled by

the object divided by the time taken to cover that distance

A marathon runner runs at a average speed of 5.33 meters per second

for the first 3600 seconds

⇒ His speed = 5.33 m/s

⇒ For time = 3600 seconds

Then he runs at a speed of 5.00 meters per second for the next

4200 seconds

⇒ His speed is 5 m/s

⇒ For time 4200 seconds

Average speed = total distance : total time

Lets find the total distance

Distance = speed * time

⇒ The 1st distance = 5.33 * 3600 = 19188 meters

⇒ The 2nd distance = 5 * 4200 = 21000 meters

⇒ Total distance = 19188 + 21000 = 40188 meters

Lets find the total time

⇒ Total time = 3600 + 4200 = 7800 seconds

⇒ Average speed = 40188 : 7800 = 5.15 m/s

The average speed of the marathon runner is 5.15 meters per second