4.28. Set Up:Neglect air resistance. No object is in contact with the stone.Solve:The free-body diagram is the same as for (a), (b), and (c) and is shown in Figure 4.28. The only force is thedownward force of gravity.Figure 4.284.29. Set Up:The brakes cause a friction force from the road that is directed opposite to the motion.Solve: (a)The free-body diagram is shown in Figure 4.29a. wis the gravity force,nis the normal force and is thefriction force. The friction force is directed opposite to the direction the car is traveling.Figure 4.29(b)The free-body diagram is shown in Figure 4.29b. The force Pis applied to the passenger by the car seat and is inthe direction the car is moving.Reflect:In each case there is a net horizontal force on the object and this force produces an acceleration in the direc-tion of the net force.
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