61. CONCEPT QUESTIONSa. Since the speed and mass are constant and the radius is fixed, the centripetal force is the same at each point on the circle. b. When the ball is at the three o’clock position, the force of gravity, acting downward, is perpendicular to the string and cannot contribute to the centripetal force. (See Figure 5.21, point 2 for a similar situation.) At this point, only the tension of T= 16 N contributes to the centripetal force. Considering that the centripetal force is the same everywhere, we can conclude that it has a value of 16 N everywhere. c. At the twelve o’clock position the tension Tand the force of gravity mgboth act downward (the negative direction) toward the center of the circle, with the result that the centripetal force at this point is –T– mg. (See Figure 5.21, point 3.) The magnitude of the centripetal force here, then, is T+ mg. At the six o’clock position
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