# hw14 - khounvivongsy(sk27799 – Homework 14 – Weathers...

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Unformatted text preview: khounvivongsy (sk27799) – Homework 14 – Weathers – (17104) 1 This print-out should have 13 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The speed of a moving bullet can be deter- mined by allowing the bullet to pass through two rotating paper disks mounted a distance 98 cm apart on the same axle. From the angular displacement 21 ◦ of the two bullet holes in the disks and the rotational speed 821 rev / min of the disks, we can determine the speed of the bullet. 21 ◦ v 821 rev / min 98 cm What is the speed of the bullet? Correct answer: 229 . 88 m / s. Explanation: Let : ω = 821 rev / min , d = 98 cm , and θ = 21 ◦ . θ = ω t t = θ ω , so the speed of the bullet is v = d t = dω θ = (98 cm) (821 rev / min) 21 ◦ × 360 ◦ 1 rev 1 m 100 cm 1 min 60 s = 229 . 88 m / s . keywords: 002 10.0 points A wheel starts from rest at t = 0 and rotates with a constant angular acceleration about a fixed axis. It completes the first revolution in 2 . 9 s. How long after t = 0 will the wheel com- plete the second revolution? Correct answer: 4 . 10122 s. Explanation: Let : t 1 = 2 . 9 s , θ 1 = 1 rev , and θ 2 = 2 rev . The wheel starts from rest, so θ = θ + 1 2 αt 2 = 1 2 αt 2 ∝ t 2 . Thus θ 2 θ 1 = t 2 2 t 2 1 t 2 = radicalbigg θ 2 θ 1 t 1 = radicalbigg 2 rev 1 rev (2 . 9 s) = 4 . 10122 s . 003 10.0 points A bicycle is turned upside down while its owner repairs a flat tire. A friend spins the other wheel of radius 0 . 4 m and observes that drops of water fly off tangentially. She mea- sures the height reached by drops moving ver- tically. A drop that breaks loose from the tire on one turn rises 83 . 8 cm above the tangent point. A drop that breaks loose on the next turn rises 81 . 7 cm above the tangent point khounvivongsy (sk27799) – Homework 14 – Weathers – (17104) 2 (the angular speed of the wheel is decreas- ing). h . 4 m radius ω Find the angular deceleration of the wheel. The acceleration of gravity is 9 . 8 m / s 2 . As- sume the angular deceleration is constant....
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hw14 - khounvivongsy(sk27799 – Homework 14 – Weathers...

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