"The wheels of a certain roller coaster are both above and below the rails so that the car will not leave the rails. The mass supported by this particular wheel is 402 kg and the radius of this section of track is 70 m. What is the magnitude of the force that the track exerts on the wheel when the speed of the car is 45 m/s?" I'm not sure where to go. I've tried finding the centripetal acceleration and multiplying it by 402, but it was wrong. I have a FBD but don't know what to do from here.