If we approximate the rack to be completely flat and the racecar is travelling a constant 30.5 m/s around the turn, what forces are responsible for the centripetal acceleration?

We have,

The race car is travelling a constant 30.5 m/s around the turn. When the car is travelling around a turn, the centripetal force acts on it. The centripetal force is balanced by the force of friction between the car and the surface. Hence, frictional force is responsible for the centripetal acceleration.

i am pretty sure it is c because when people are closer together, they cannot move as freely. picture being in a mostly full elevator, for instance. the people are right next to you, and you can barely move.

neither accurate nor precise.