Conical sand pile with a bottom area of 7.2 square meters and a height of 2 meters.

Bottom radius =√7.2/π

∴ stacking angle of sand pile =arctan[2/(√7.2/π)]≈52.87?

Due to the existence of friction self-locking, there is a maximum "accumulation angle" in the sand pile, which is scientifically called "angle of repose" (that is, under the condition of fixed bottom area, the pile height has a maximum value and it is impossible to accumulate indefinitely), and the angle of repose of dry sand is 30 ~ 35? , wet sand is 45? And in this problem, the stacking angle of sand piles is much larger than 45? There is no such sand pile. Do parents think too much?