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Unformatted text preview: homework 13 HETTIGER, CHRISTOF Due: Feb 19 2008, 4:00 am 1 Question 1, chap 6, sect 2. part 1 of 1 10 points A load of 63 N attached to a spring hanging vertically stretches the spring 5 . 2 cm. The spring is now placed horizontally on a table and stretched 10 cm. What force is required to stretch it by this amount? Correct answer: 121 . 154 N (tolerance 1 %). Explanation: Given : F = 63 N , x 1 = 5 . 2 cm , and x 2 = 10 cm . The force exerted by the spring is F 1 = k x 1 k = F 1 x 1 . When stretched 10 cm, F 2 = k x 2 = F 1 x 2 x 1 = (63 N) (10 cm) 5 . 2 cm = 121 . 154 N . Question 2, chap 6, sect 2. part 1 of 2 10 points A 0 . 525 kg mass is attached to a spring with a spring constant 145 N / m so that the mass is allowed to move on a horizontal frictionless surface. The mass is released from rest when the spring is compressed 0 . 104 m. Find the maximum force on the mass. Correct answer: 15 . 08 N (tolerance 1 %). Explanation: Basic Concepts: F = ma F = k x The maximum force and acceleration occur at the maximum amplitude of the motion. Solution: The force on the mass is F = k x = (145 N / m) (0 . 104 m) = 15 . 08 N . Question 3, chap 6, sect 2. part 2 of 2 10 points Find the maximum acceleration. Correct answer: 28 . 7238 m / s 2 (tolerance 1 %). Explanation: The acceleration is a = F m = 15 . 08 N . 525 kg = 28 . 7238 m / s 2 . Question 4, chap 6, sect 3. part 1 of 2 10 points The coefficient of static friction between the person and the wall is 0 . 76 . The radius of the cylinder is 6 . 44 m . The acceleration of gravity is 9 . 8 m / s 2 . An amusement park ride consists of a large vertical cylinder that spins about its axis fast enough that any person inside is held up against the wall when the floor drops away. 6 . 44 m What is the minimum angular velocity min needed to keep the person from slip ping downward? Correct answer: 1 . 41502 rad / s (tolerance 1 %). Explanation: homework 13 HETTIGER, CHRISTOF Due: Feb 19 2008, 4:00 am 2 Let : R = 6 . 44 m and = 0 . 76 ....
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