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Question

Two people, A and B, start running from the same point on a circular track of length 400 meters, but in opposite directions. A runs at 6 m/s and B at 4 m/s. In how many seconds will they meet for the first time?

The correct answer is
40 seconds

Circular Track Meeting Time Calculation

This problem involves calculating the time it takes for two runners, moving in opposite directions on a circular track, to meet for the first time. We can solve this using the concept of relative speed.

Key Information

  • Track Length = 400 meters
  • Speed of Runner A ($v_A$) = 6 m/s
  • Speed of Runner B ($v_B$) = 4 m/s
  • Direction: Opposite

Relative Speed Concept

When two objects move in opposite directions, their relative speed is the sum of their individual speeds. This is the speed at which the distance between them decreases.

Relative Speed ($v_{rel}$) = $v_A + v_B$

In this case, $v_{rel} = 6 \text{ m/s} + 4 \text{ m/s} = 10 \text{ m/s}$.

Calculating Meeting Time

For the runners to meet for the first time, the total distance covered by both combined must equal the length of the circular track.

Time = Total Distance / Relative Speed

Time = $\frac{\text{Track Length}}{v_{rel}}$

Time = $\frac{400 \text{ meters}}{10 \text{ m/s}}$

Time = 40 seconds

Conclusion

The runners will meet for the first time after 40 seconds.

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Important Questions from Speed Time and Distance

  1. A train travelling at a speed of 72 km/hr crosses a post in 20 seconds. If it crosses another train travelling at a speed of 54 km/hr in the same direction in 1 minute 45 seconds, then the difference in length between the two trains is

  2. Rajiv's boat can travel along the current at the 8 km/hour and against the current at the rate 6 km/hour. Find the time taken by the boat to sail 28 km in still water.

  3. Rohit and Dinesh are 64 km apart. Rohit can walk at a speed of 15 km/hr and Dinesh at the speed of 17 km/hr. In how many hours will they meet if they are travelling towards each other?

  4. Two trains running in opposite directions cross a man standing on the platform in 25 seconds and 32 seconds respectively and they cross each other in 30 seconds. The ratio of their speed is:

  5. A worker covers a distance of 81 km in 11 hours. He travels partly on foot at 4.5 km/h and partly on bicycle at 15 km/h. What is the distance covered on the cycle?

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