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GOAL Calculate the frictional force that causes an object to have a centripetal acceleration.
PROBLEM A car travels at a constant speed of 30.0 mi/h (13.4 m/s) on a level circular turn of radius 50.0 m, as shown in the bird’s-eye view in Figure 7.11a. What minimum coefficient of static friction, μ_s, between the tires and roadway will allow the car to make the circular turn without sliding?
STRATEGY In the car’s free-body diagram (Fig. 7.11b) the normal direction is vertical and the tangential direction is into the page (Step 2). Use Newton’s second law. The net force acting on the car in the radial direction is the force of static friction toward the center of the circular path, which causes the car to have a centripetal acceleration. Calculating the maximum static friction force requires the normal force, obtained from the normal component of the second law.