The problem: A car traveling on a flat (unbanked) circular track accelerates uniformly from rest with a tangential acceleration of 1.60 m/s2. The car makes it one quarter of the way around the circle before it skids off the track. Determine the coefficient of static friction between the car and track from these data. I keep ending up with acceleration_radial = PI*acceleration_tangential, and thus u = PI*acceleration_tangential/g = ~0.513. My assignment says that it is wrong.