A car of mass \( m \) is traveling at a constant speed \( v \) around a flat, horizontal circular track of radius \( R \). The coefficient of static friction between the car's tires and the road is \( \mu_s \). The car does not slip as it moves around the track. Which of the following expressions correctly represents the magnitude of the static friction force \( f_s \) exerted by the road on the car?