Here's the question:
A Ferris wheel (d=50ft) makes 1 revolution/40 sec. If the center of the wheel is 30ft above the ground, how long after reaching the lowest point is a rider 50 ft above the ground?
I've tried a number of things, but I realize I'm probably just having trouble figuring out the arc length from the bottom of the wheel to the point where the rider's height from the bottom is 45. The y-value thing makes me think I need a sin-inverse. I thought it might be 45/50pi, but that's greater than 1. Basically, please help me find the arc length from the bottom of the wheel to where the y-value of the point is 45.