Question

A runner runs 300 m at an average speed of 3.0 m/s. She then runs another 300m at an average
speed of 6.0 m/s.
What is her average speed for the total distance of 600m?
A 2.0 m/s
B 4.0 m/s
C 4.5 m/s
D 8.0 m/s​

Answer 1

Answer:

B. 4 m/s

Explanation:

v=d/t

Running for 300 m at 3 m/s takes 100 seconds and running at 300 m at 6 m/s takes 50 seconds. 100 s + 50 s = 150 s (total time). Total distance is 600 m, so 600 m/ 150 s = 4 m/s.

Answer 2

The average speed of the runner for the entire journey is 4 m/s.

The given parameters;

• distance covered by the runner, s = 300 m
• initial speed of the runner, v₁ = 3 m/s
• final speed of the runner, v₂ = 6 m/s
• total distance covered by the runner, = 600 m

The average speed of the runner is obtained by diving the total distance covered by the runner by the total time of motion as shown below;

$average \ speed = \frac{total \ distance }{total \ time \ of \ motion}$

The time of motion during the first distance covered;

$t_1 = \frac{300}{3} = 100 \ s$

The time of motion during the second distance covered;

$t_2 = \frac{300}{6} = 50 \ s$

The average speed is calculated as;

$average \ speed = \frac{600}{100 + 50} \\\\average \ speed = 4 \ m/s$

Thus, the average speed of the runner for the entire journey is 4 m/s.

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