Question

Ivy is competing in a 400 m race.

She runs at a constant speed of 5.4 m/s for the first 150 m, then 4.5 m/s for 40 seconds.
The remainder of the race takes her 34 seconds to complete.
What is Ivy's average speed for the entire race to 1 dp?

Answer 1

4.5m/s

Explanation:

4.5x40=180

180+150=330

400-330=70

70/34=2.05882352941

(2.05882352941x70)+(5.4x150)+(4.5x180)=1791.11764706

1791.11764706/400=4.47779411765

4.47779411765=4.5

4.5m/s

Answer 2

Average speed = 3.9 m /s

Explanation:

Total distance = 400m

First 150m = 5.4m/s

`speed = (distance)/(time) \\\\time = (distance)/(speed) = (150)/(5.4) = 27.78 \ s`

Second part :

S = 4.5m/s for 40s

`Distance = speed * time = 4.5 * 40 = 180 \ m`

Third part :

Remaining distance = 400 - 150 -180 = 70m

Time taken to cover it = 34s

`speed = (distance)/(time) = (70)/(34) = 2.05 \`

Speed = 2.05m/s

Find average speed

`Average\ speed = (total \ distance )/(total \ time \ taken ) \\\\Average \ speed = (400)/(101.78) = 3.93 \ mps`

Round to 1 dp => average speed = 3.9m /s