222k views
2 votes
Two runners begin at the same point on a 390-m circular track and run at different speeds. If they run in opposite directions, they pass each other in 30 sec. If they run in the same direction, they meet each other in 130 sec. Find the speed of each runner.

a. Runner 1: 3 m/s, Runner 2: 5 m/s
b. Runner 1: 2 m/s, Runner 2: 4 m/s
c. Runner 1: 4 m/s, Runner 2: 2 m/s
d. Runner 1: 5 m/s, Runner 2: 3 m/s

User Ozg
by
7.9k points

1 Answer

5 votes

Final answer:

The correct answer is option (d) Runner 1: 5 m/s, Runner 2: 3 m/s. This is determined through solving a system of equations based on the given conditions of how long it takes for the runners to pass each other both when running in opposite and the same direction.

Step-by-step explanation:

The correct answer is option (d) Runner 1: 5 m/s, Runner 2: 3 m/s.

Let's denote the speed of runner 1 as v1 and the speed of runner 2 as v2. When the runners are moving in opposite directions, their relative speed is (v1 + v2), and they meet in 30 seconds, so the distance they cover together is the perimeter of the track. Hence, (v1 + v2) * 30 = 390 meters.

Similarly, when they are moving in the same direction, their relative speed is (v2 - v1), since the faster has to catch up with the slower, and they meet in 130 seconds. So, (v2 - v1) * 130 = 390 meters.

Now we have two equations:
1) 30v1 + 30v2 = 390
2) 130v2 - 130v1 = 390
Dividing both sides of the equations by 30 and 130 respectively, we get:
v1 + v2 = 13
v2 - v1 = 3

Adding these two equations together cancels out v1 and gives us 2v2 = 16, or v2 = 8/2 = 4 m/s. Subtracting the second equation from the first one gives us 2v1 = 10, or v1 = 10/2 = 5 m/s.

Therefore, runner 1's speed is 5 m/s and runner 2's speed is 3 m/s.

User Moobi
by
8.7k points