An old phonograph record accelerates from rest to a final angular velocity of 78
ID: 2004139 • Letter: A
Question
An old phonograph record accelerates from rest to a final angular velocity of 78.0 rpm (revolutions per minute) in 0.350 s. The record has a radius of 15.0 cm.a. Express the final angular velocity in units of rad/s.
b. What is the angular acceleration of the record during this time?
c. A dust speck lies 8.36 cm from the center of the record. What is the final speed of the speck?
d. Through what total angle does the record rotate as it accelerates?
e. What is the tangential acceleration of the speck during this time?
Explanation / Answer
a. Express the final angular velocity in units of rad/s.
78 rpm = 78(2) radians/ min = 78(2) radians/ min x 1 min/60 sec = 2.6 radians/sec
b. What is the angular acceleration of the record during this time?
a = v/t = v/t = (2.6 – 0)/(0.350 – 0) = 10.4 rad/s²
c. A dust speck lies 8.36 cm from the center of the record. What is the final speed of the speck?
One rev for the spec is 2(8.36) cm = 16.72 cm 16.72 cm/rev
78 rpm = 1.3 rev/s
speed of spec is 16.72 cm/rev x 1.3 rev/s = 21.736 cm/s
d. Through what total angle does the record rotate as it accelerates?
angular d = angular a x time² = 10.4 rad/s² x (0.350 s)² = 1.274 radians.
e. Tangential acceleration = angular acceleration x cos