Please Help solve this question

Question

Suppose the coefficient of static friction between a dime and the back wall of a rocket car is 0.311. At what minimum rate (in m/s²) would the car have to accelerate so that a dime placed on the back wall would remain in place?

Answer 1

µma ≥ mg; a ≥ g/µ; a_min= g/µ = 9.8m/s²/0.311 = 31.5 m/s²