Kiran swims in a 90 m long pool. He covers a total distance of 360 m in 2 minutes by swimming from one end to the other and back along the same straight path twice. What is Kiran’s average speed (in m/s)?

Introduction / Context:
This question is about average speed in a swimming pool. Kiran swims back and forth along a straight path in a 90 m pool, making multiple lengths, and we are given his total distance and total time. We must compute his average speed in metres per second. Such problems are designed to reinforce the basic definition of average speed and to ensure that students can handle unit conversions between minutes and seconds correctly.

Given Data / Assumptions:
- Length of the pool = 90 m.
- Kiran swims from one end to the other and back along the same straight path twice, covering 360 m total.
- Total time taken = 2 minutes.
- Speeds are taken as uniform for the purpose of computing average speed, even though real swimmers may vary speed slightly.

Concept / Approach:
The key concept is the definition of average speed:
average speed = total distance / total time.
Here, the total distance is given directly as 360 m. However, the time is given in minutes, while the desired unit for speed is metres per second, so we need to convert 2 minutes into seconds first. Once both total distance and total time are in compatible units, we can compute a single ratio to get the average speed.

Step-by-Step Solution:
Step 1: Confirm the total distance.Each full length of the pool is 90 m. Going from one end to the other and back is 2 * 90 = 180 m.Doing this twice gives 2 * 180 = 360 m, which matches the statement.Step 2: Convert total time into seconds.Total time = 2 minutes = 2 * 60 = 120 seconds.Step 3: Apply the average speed formula.Average speed = total distance / total time = 360 m / 120 s = 3 m/s.

Verification / Alternative check:
We can think: if Kiran swims at 3 m/s, then in 120 seconds he would cover 3 * 120 = 360 m, exactly matching the total distance stated. If his speed were 4 m/s, he would cover 480 m in 2 minutes, which is too much, and if it were 2 m/s, he would cover only 240 m, which is too little. Therefore, 3 m/s is the only value consistent with the given numbers.

Why Other Options Are Wrong:
- 4 m/s would imply a total distance of 480 m in 2 minutes, greater than the 360 m given.
- 6 m/s would correspond to 720 m in 2 minutes, which is clearly impossible for this problem setup.
- 8 m/s is even higher and unrealistically large for both the numbers and a typical swimming speed.

Common Pitfalls:
One common mistake is to forget to convert minutes into seconds, leading to a speed computed as metres per minute instead of metres per second. Another pitfall is to misunderstand the description of the back-and-forth motions and miscalculate the total distance. Carefully counting the number of lengths and converting time units correctly ensures an accurate solution.

Final Answer:
Kiran’s average speed is 3 m/s.