Water weight figures in jetpack dynamics

Vonk and Bohacek reply: We’d like to clarify two points that weren’t explicit in our Quick Study. First, between the watercraft and the jetpack, the extra hose simply floats near the river’s surface. Because the floating portion of the hose cannot support any additional weight without sinking, the full weight of the water above the river’s surface must be supported from above. Second, the initial velocity of the water from the personal watercraft is horizontal. Thus the water must be accelerated upward by the upward-curving hose, which exerts an additional downward force on the jetpack. In the end, the downward force exerted by the hose water on the jetpack is greater than, not less than, the simplified calculation in the Quick Study.