Michelle T. answered 12/20/20
Caltech/UCSD Engineer turned Educator (University and High School)
For this problem, the friction force is providing the centripetal force, so the friction force magnitude has to be at least as big as the centripetal force magnitude. From the radius, speed, and mass, we can find the centripetal force. The centripetal force is equal to the minimum friction force we need.
Centripetal force:
F = mv2/r = (146 kg)(12.1 m/s)2/(87.8 m) = 243 N
So you need at least 243 N of friction force.