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A disc rotates about its central axis with constant angular acceleration starting from rest. At a certain instant its angular speed is 12 rad/s, and after an additional angular displacement of 80 radians the angular speed becomes 28 rad/s. How much time (in seconds) does the disc take to complete this additional angular displacement of 80 radians?
- 2 s
- 4 s
- 5 s
- 8 s
Correct answer: 4 s
Solution
From omega2² - omega1² = 2*alpha*theta: alpha = (784-144)/(2*80) = 4 rad/s². Then t = (omega2 - omega1)/alpha = (28-12)/4 = 4 s.
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