A woman places her briefcase on the backseat of her car. As she drives to work, the car negotiates an unbanked curve in the road that can be regarded as an arc of a circle of radius 54.5 m. While on the curve, the speed of the car is 12.4 m/s at the instant the briefcase starts to slide across the backseat toward the side of the car. What force causes the centripetal acceleration of the briefcase when it is stationary relative to the car? Under what condition does the briefcase begin to move relative to the car?

The force that cause the centripetal acceleration is the static friction, and the briefcase begin to move if the force of centripetal acceleration exceeds the force due to the static friction

Explanation:

Given data:

r = radius = 54.5 m

v = speed of the car = 12.4 m/s

The force due to the static friction that is exerted on the curve in the road is what causes the centripetal acceleration. If the force due to centripetal acceleration is greater than the force of static friction, then the briefcase will begin to roll.