Yasir and Priya are standing on a beach with their friend Min-jun, who is holding a bright red flag. Yasir, who is taller than Priya, suggests that they wade into the ocean to see how deep they can go before the water reaches their shoulders. As Yasir and Priya walk parallel to each other into the ocean, Priya, being shorter, reaches shoulder-depth water first. They both stop at this point and wave to Min-jun, who is watching from the beach. Given that Yasir is taller, his waist is aligned with Priya's chest. From Min-jun's perspective on the beach, aligned with Yasir and Priya, who are a significant distance away in the water, does the red flag appear higher or lower than Priya's head and Yasir's waist? Why would it appear that way to Min-jun?
When Yasir and Priya stop in the water with Priya's shoulder submerged, the level of the water relative to their bodies will differ due to their height difference. Yasir's waist being aligned with Priya's chest indicates that the water reaches lower on Yasir's body compared to Priya's. Now considering Min-jun's perspective from the beach with the red flag in hand, spatial reasoning can be used to understand how the flag's position appears relative to Yasir's and Priya's submerged bodies.

If Min-jun is holding the red flag at a height that is constant and does not change, its apparent position against the ocean's horizon will depend on several factors: the curvature of the Earth, the distance of Yasir and Priya from Min-jun, and the optical phenomena involving the atmosphere if any. However, without overcomplicating the scenario, assuming typical beach conditions and a relatively short distance between Min-jun and his friends, the spatial reasoning hinges on the line of sight.

For Min-jun, looking directly at his friends means that the field of view is limited horizontally by Yasir and Priya's width and vertically from the water's surface to the sky above them. Since Yasir's waist is at the same level as Priya's chest, from Min-jun's perspective, the red flag held at shoulder height or above would appear higher than both Yasir's waist and Priya's head. As the light travels in straight lines, Min-jun would see the flag above Yasir and Priya because it's actually above the water level they are standing in.

However, it is important to note that visual perception might slightly distort this clear-cut reasoning due to atmospheric refraction or other visual distortions, but the basic spatial reasoning stands as described. The flag remains at a fixed height which is above the water line, and thus for Min-jun, it would appear higher than the water level that has reached Priya's shoulders and Yasir's waist.