1. The problem statement, all variables and given/known data A bridge over a small river has a roadway which is in the shape of an arch having radius of curvature of 41 m. What is the maximum speed at which an automobile can travel across the bridge without leaving the bridge? 2. Relevant equations Fc = (mv^2)/r Fg= mg 3. The attempt at a solution Fnet = ma Fc = Fg - Fn (mv^2) / r = mg - fn (v^2) / r = g root ( 41 * 9.81) = 20.06 m/s I know that this is the right answer, but I don't understand why the normal force is zero. Isn't the bridge exerting a force equal to that of gravity on the car so that it doesn't go through the bridge?