5. The horizontal tumtable shown to the right rotates at a constant rate. As viewed from above. a coin on the turntable moves counterclockwise in a circle as shown. Which of the following vectors best represents the direction of the frictional force exerted on the coin by the turntable when the coin is in the position shown? (A) '- (B) + (C) / view from above (D) * (E) f 6. A motorcycle of mass 100 kg travels around a flat, circular track of radius, 10 meters with a constant speed of 20 m/s. What net force is required to keep the motorcycle moving in a circular path at this speed? (A) 200 newtons (B) 400 newtons (C) 2000 newtons (D) 4000 newtons 7. A ball of mass m is attached to the end of a string, and swings around in a vertical circle of radius r. At its highest point. the speed v of the ball is such that the tension in the string is zero. The magnitude of the acceleration of the ball, at its highest point, is (A) g (the acceleration due to gravity) (B) 9r (C) zero (D) mvzl r (E) none of the above 8. Which is common to both projectile and uniform circular motion? (A) the acceleration is constant (8) the acceleration is perpendicular to the direction of motion (C) the magnitude of the accelerations is constant (D) the direction of the acceleration is constant (E) the acceleration is proportional to the square of the velocity 9. An acrobat grasps a rope and swings in a circular arc of radius 5 meters. At the lowest point in the swing. the acrobat's speed is 9 this. At this instant the acrobat's acceleration is most nearly (A) 0 (B) 10 m/sZ, down (C) 10 m/sz, up (D) 16 W52, down (E) 16 m/sZ, up I _