Dan has an antique turntable that plays vinyl disks at 33 1/3 revolutions per mi
ID: 2048422 • Letter: D
Question
Dan has an antique turntable that plays vinyl disks at 33 1/3 revolutions per minute.a. What is the speed (in cm/s) at the outer edge of a record if that edge is 15 cm from the center of rotation?
b. While the turntable runs without the stylus or record (it is the same size as a record), a penny is carefully placed on the turntable and travels with it remaining in place. Explain whether or not there is any centripetal force on the penny.
c. Where on the turntable is the frictional force on the penny the greatest? Explain.
Explanation / Answer
Distance for one revolution = 2 pi r = 2 * pi * 15 cm = 94.25 cm Distance for 33 1/3 revolutions = 33 1/3 * 94.25 = 3141.6 cm Speed = distance / time = 3141.6 cm / 60 seconds = 52.36 cm/s b. The penny travels in a circular path, so there must be a centripetal force acting on it. The force is from friction. If there was no friction, the penny would slide off the turntable. The friction keeps the penny in place, keeps the penny in a circular path, so the friction provides the centripetal force. c. The centripetal force must be greater near the edge of the turntable, because this is where the penny is moving fastest. So the friction must be greatest at the edge (to keep the penny in place).
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