Question

Riders in a carnival ride stand with their backs against the wall of a circular room of diameter 8.0m. The room is spinning horizontally about an axis through its center at a rate of 45 rev/min when the floor drops so that it no longer provides any support for the riders. What is the minimum coefficient of static friction between the wall and the rider required so that the rider does not slide down the wall? 

(A) 0.0012 

(B) 0.056 

(C) 0.11 

(D) 0.53 

(E) 8.9  

Answer 1

Correct option (C) 0.11

F_f = mg to balance

µF_N = µmv²/r = mg, where v = 2πrf which gives µ = g/(4π²rf²)

Be careful! f is given in rev/min (45rev/min = 0.75rev/sec) and 8.0 m is the ride’s diameter