1. The problem statement, all variables and given/known data An airplane flies in a loop (a circular path in a vertical plane) of radius 120m . The pilot's head always points toward the center of the loop. The speed of the airplane is not constant; the airplane goes slowest at the top of the loop and fastest at the bottom. At the top of the loop, the pilot feels weightless. What is the speed of the airplane at this point? 2. Relevant equations F = mv2/r 3. The attempt at a solution n + w = mv2/r v = sqrt(gr) = 34.3 m/s I was able to solve this problem using F = mv2/r, but I'm confused to why it worked. Doesn't this formula only apply to situations in which the speed is constant?