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Unformatted text preview: homework 09 – VENNES, ROSS – Due: Nov 2 2007, 1:00 am 1 Question 1, chap 12, sect 2. part 1 of 2 10 points A record has an angular speed of 44 . 2 rev / min. What is its angular speed? Correct answer: 4 . 62862 rad / s (tolerance ± 1 %). Explanation: 1 rev = 6 . 28319 rad, and 1 min = 60 s , Therefore, ω 1 = (44 . 2 rev / min) parenleftbigg 2 π rad rev parenrightbiggparenleftbigg 1 min 60 s parenrightbigg = 4 . 62862 rad / s . Question 2, chap 12, sect 2. part 2 of 2 10 points Through what angle, in radians, does it rotate in 1 . 41 s? Correct answer: 6 . 52635 rad (tolerance ± 1 %). Explanation: θ = ω t = (4 . 62862 rad / s) (1 . 41 s) = 6 . 52635 rad . Question 3, chap 12, sect 2. part 1 of 2 10 points A racing car travels on a circular track of radius 335 m. The car moves with a constant linear speed of 42 . 4 m / s. Find its angular speed. Correct answer: 0 . 126567 rad / s (tolerance ± 1 %). Explanation: The linear speed v and the angular speed ω are related by, v = R ω ⇒ ω = v R . Question 4, chap 12, sect 2. part 2 of 2 10 points Find the magnitude of its acceleration. Correct answer: 5 . 36645 m / s 2 (tolerance ± 1 %). Explanation: If the car is moving at a constant speed, there is no tangential acceleration, thus the acceleration is purely radial, a r = v 2 R . Question 5, chap 12, sect 2. part 1 of 1 10 points A woman passes through a revolving door with a tangential speed of 1.8 m/s. If she is 0.78 m from the center of the door, what is the door’s angular speed? Correct answer: 2 . 30769 rad / s (tolerance ± 1 %). Explanation: Basic Concept: v t = rω Given: v t = 1 . 8 m / s r = 0 . 78 m Solution: ω = v t r = 1 . 8 m / s . 78 m = 2 . 30769 rad / s Question 6, chap 12, sect 2. part 1 of 1 10 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 64 . 5 cm apart on the same axle. From the homework 09 – VENNES, ROSS – Due: Nov 2 2007, 1:00 am 2 angular displacement 48 ◦ of the two bullet holes in the disks and the rotational speed 866 rev / min of the disks, we can determine the speed v of the bullet. 48 ◦ v 866 rpm 64 . 5 cm What is the speed of the bullet? Correct answer: 69 . 8212 m / s (tolerance ± 1 %). Explanation: Let : ω = 866 rev / min , d = 64 . 5 cm , and θ = 48 ◦ . From θ = ω t the time to pass through an angle θ is t = θ ω = (48 ◦ ) (90 . 6873 rad / s) π rad 180 ◦ = 0 . 00923788 s . Then the speed of the bullet is v = d t = (64 . 5 cm) (0 . 01 m / cm) . 00923788 s = 69 . 8212 m / s . Question 7, chap 12, sect 2. part 1 of 3 10 points A car accelerates uniformly from rest and covers a distance of 53 m in 6 . 9 s....
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This homework help was uploaded on 04/18/2008 for the course PHY 303K taught by Professor Turner during the Spring '08 term at University of Texas at Austin.
 Spring '08
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