# HW 11 - johnson(mjj622 HW 11 Coker(56625 This print-out...

This preview shows pages 1–3. Sign up to view the full content.

johnson (mjj622) – HW 11 – Coker – (56625) 1 This print-out should have 15 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. This assignment covers the fairly short Ch. 12, dealing with rigid body rotation, rota- tional inertia and rotational kinetic energy. 001 10.0 points The tub of a washer goes into its spin-dry cycle, starting from rest and reaching an an- gular speed of 2 rev / s in 3 . 2 s . At this point the person doing the laundry opens the lid, and a safety switch turns off the washer. The tub slows to rest in 6 . 4 s . Through how many revolutions does the tub turn? Assume constant angular accelera- tion while it is starting and stopping. Correct answer: 9 . 6 rev. Explanation: Let : ω 0 = 0 rev / s , ω 1 = 2 rev / s , Δ t 1 = 3 . 2 s , ω 2 = 0 rev / s , and Δ t 2 = 6 . 4 s . θ = ω av Δ t = ω i + ω f 2 Δ t = ω 1 2 Δ t in each case since either the initial or final speed is zero. While speeding up, θ 1 = 2 rev / s 2 (3 . 2 s) = 3 . 2 rev and while decelerating, θ 2 = 2 rev / s 2 (6 . 4 s) = 6 . 4 rev , so θ = θ 1 + θ 2 = 3 . 2 rev + 6 . 4 rev = 9 . 6 rev . 002 (part 1 of 2) 10.0 points A disk with a radius of 0.1 m is spinning about its center with a constant angular speed of 10 rad/sec. What are the speed and magnitude of the acceleration of a bug clinging to the rim of the disk? 1. 0.1 m/s and 1 m/s 2 2. 10 m/s and 10 m/s 2 3. 1 m/s and 10 m/s 2 correct 4. 1 m/s and 0 m/s 2 (Disk spins at constant speed.) Explanation: The speed of the bug is v = R ω = (0 . 1 m)(10 1 / s) = 1 m / s and its acceleration is a r = R ω 2 = (0 . 1 m)(10 1 / s) 2 = 10 m / s 2 . 003 (part 2 of 2) 10.0 points Let the turntable spin faster and faster, with constant angular acceleration vectorα . Which sketch qualitatively shows the direc- tion of the acceleration vector vectora of the bug? 1. vectora 2. vectora

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
johnson (mjj622) – HW 11 – Coker – (56625) 2 3. vectora correct 4. vectora Explanation: The bug has an acceleration vectora r directed toward the center of the circle, and an accel- eration vectora t in the same direction as its velocity (counterclockwise); the net acceleration is the vector sum of vectora r and vectora t . 004 10.0 points A disk is spinning about an axis through its center of mass, and at a given moment has an angular velocity vector vectorω as shown.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern