hw11 - karna(pk4534 HW 11 coker(58245 This print-out should...

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karna (pk4534) – HW 11 – coker – (58245) 1 This print-out should have 16 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 (part 1 of 2) 10.0 points A wheel starts from rest and rotates with constant angular acceleration to an angular speed of 17 . 9 rad / s in 2 . 32 s. Find the magnitude of the angular acceler- ation of the wheel. Correct answer: 7 . 71552 rad / s 2 . Explanation: Let : Δ ω = 17 . 9 rad / s and Δ t = 2 . 32 s . Angular acceleration is α = Δ w Δ t = 17 . 9 rad / s 2 . 32 s = 7 . 71552 rad / s 2 . 002 (part 2 of 2) 10.0 points Find the angle in radians through which it rotates in this time. Correct answer: 20 . 764 rad. Explanation: The angle through which the wheel rotates during this time interval is θ = 1 2 α t 2 = 1 2 (7 . 71552 rad / s 2 ) (2 . 32 s) 2 = 20 . 764 rad . keywords: 003 10.0 points At t = 0, a wheel rotating about a fixed axis at a constant angular deceleration of 0 . 22 rad / s 2 has an angular velocity of 4 . 1 rad / s and an angular position of 9 . 5 rad. What is the angular position of the wheel after 4 s? Correct answer: 24 . 14 rad. Explanation: Let : α = 0 . 22 rad / s 2 , ω 0 = 4 . 1 rad / s , θ 0 = 9 . 5 rad , and t = 4 s . The angular position is θ f = θ 0 + ω 0 t + 1 2 α t 2 = 9 . 5 rad + (4 . 1 rad / s) (4 s) + 1 2 ( 0 . 22 rad / s 2 ) (4 s) 2 = 24 . 14 rad . 004 10.0 points Unlike a phonograph record that has a con- stant angular speed, a CD scans information at a constant linear speed (130 cm/s). Does the CD rotate at a constant or varying angular speed? 1. varying angular speed correct 2. constant angular speed Explanation: v = r ω Since the radius changes, the angular speed must change to keep the linear speed of the scanning head constant. 005 10.0 points A horizontal disk with a radius of 15 m ro- tates about a vertical axis through its center. The disk starts from rest and has a constant angular acceleration of 3 . 9 rad / s 2 . At what time will the radial and tangen- tial components of the linear acceleration of a point on the rim of the disk be equal in mag- nitude?
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