Since we're dealing with radial acceleration around a circle, I used the radial acceleration equation a=v²/r. At the top of the hill, the force upward exerted by the hill is less than the weight of the sled. if v is large enough the term (g-v²/r) will become 0 and the sled will fly off the ground as it reaches the peak. Let me know if I can clarify any of my work.
