Question

Kimberley is taking part in a race. For the first 160 m she runs at 4 m/s. The remaining 420 m of the race takes her 120 seconds. What is Kimberley's average speed, in m/s, over the whole race? If your answer is a decimal, give it to 2 d.p.​

Answer 1

Kimberley's speed for the first 160 m is 4 m/s.

The remaining 420 m of the race takes her 120 seconds, which is an average speed of 420 m / 120 s = 3.5 m/s.

The average speed over the whole race is the total distance traveled divided by the total time taken.

The total distance traveled is 160 m + 420 m = 580 m.

The total time taken is 120 s + the time taken to run the first 160 m at 4 m/s, which is 120 s + (160 m / 4 m/s) = 120 s + 40 s = 160 s.

Therefore, Kimberley's average speed over the whole race is 580 m / 160 s = 3.63 m/s.