A roller coaster is designed so that a car goes through a circular loop with a radius of 20m at a constant speed. That speed is set so that riders feel no push from the seat when they are at the top of the loop - that is, the acceleration due to gravity is exactly enough to keep the riders moving in a circle.

What is the speed of the car?

At the bottom of the loop, the seat will push up on the rider both to match the weight of the rider and to provide the acceleration which will turn the rider around in a circle. What acceleration does the rider feel from the seat? (hint: combine acceleration due to gravity and the centripetal acceleration)