3 EVALUATE THE ANSWER Are the units correct? Dimensional ana squared and FT is in newtons. Do the signs make sense? The signs should all be positive. Are the magnitudes realistic? The force is almost three times the weigh and the acceleration is almost three times that of gravity, which is reasona such a light object. PRACTICE PROBLEMS PRACTICE PROBLEMS 12. A runner moving at a speed of 8.8 m/s rounds a bend with a radius of 25 m. What is the centripetal accel- eration of the runner, and what agent exerts the centripetal force on the runner? 13. An airplane traveling at 201 m/s makes a turn. What is the smallest radius of the circular path (in kilometers) the pilot can make and keep the centripetal accelera- tion under 5.0 m/s? 14. A 45-kg merry-go-round worker stands on the ride's platform 6.3 m from the center, as shown in Figure 11. If her speed (Vworker) as she goes around the circle is 4.1 m/s, what is the force of friction (F+) necessary to keep her from falling off the platform?dbirlw quan 15. A 16-g ball at the end of a 1.4-m string is swung in a horizontal circle. It revolves once every 1.09 s. What is the magnitude of the string's tension? 162 Chapter 6 Motion in Two Dimensions 4 5 Do additional problems. Online Vworker Figure 11 Worker Fbao amoldo1 16. CHALLENGE A car racing on a flat track travels at 22 m/s around a curve with a 56-m radius. Find the car's centripetal acceleration. What minimum coef- ficient of static friction between the tires and the road is necessary for the car to round the curve without slipping?