quiz3 - Muraj, Hamza Quiz 3 Due: Apr 5 2006, 10:00 pm Inst:...

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

View Full Document Right Arrow Icon
Muraj, Hamza – Quiz 3 – Due: Apr 5 2006, 10:00 pm – Inst: Florin 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. The due time is Central time. 001 (part 1 o± 1) 10 points The tub o± a washer goes into its spin-dry cycle, starting ±rom rest and reaching an an- gular speed o± 3 . 4 rev / s in 5 s . At this point the person doing the laundry opens the lid, and a sa±ety switch turns o² the washer. The tub slows to rest in 11 . 5 s . Through how many revolutions does the tub turn? Assume Constant angular acceleration while it is starting and stopping. Correct answer: 28 . 05 rev. Explanation: We will break the motion into two stages: (1) an acceleration period and (2) a deceleration period. While speeding up, θ 1 = ω t = 0 + ω 2 t 1 = 1 2 ω t 1 = 1 2 (3 . 4 rev / s) (5 s) = 8 . 5 rev . While slowing down, θ 2 = ω t = ω + 0 2 t 2 = 1 2 ω t 2 = 1 2 (3 . 4 rev / s) (11 . 5 s) = 19 . 55 rev . So θ = θ 1 + θ 2 = (8 . 5 rev) + (19 . 55 rev) = 28 . 05 rev . 002 (part 1 o± 1) 10 points Assume: When the disk lands on the sur±ace it does not bounce. The disk has mass m and outer radius R with a non-uni±orm radial mass distribution so that its moment o± inertia I = 5 6 m R 2 . A disk is given a hard kick along a hori- zontal sur±ace. The kicking ±orce acts along a horizontal line through the disk’s center, so the disk acquires a linear velocity v 0 but no angular velocity. The kinetic ±riction ±orce between the sur- ±ace and the disk slows down its linear motion while at the same time making the disk spin on its axis at an accelerating rate. Eventually, the disk’s rotation catches up with its linear motion, and the disk begins to roll without slipping on the sur±ace. The acceleration o± gravity is g . I = 5 6 m R 2 R , radius m v 0 μ How long Δ t does it take ±or the ball to roll without slipping? 1. Δ t = 2 5 v 0 μ g 2. Δ t = 4 11 v 0 μ g 3. Δ t = 7 16 v 0 μ g 4. Δ t = 8 17 v 0 μ g 5. Δ t = 1 3 v 0 μ g 6. Δ t = 3 7 v 0 μ g 7. Δ t = 5 11 v 0 μ g correct 8. Δ t = 1 2 v 0 μ g
Background image of page 1

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

View Full DocumentRight Arrow Icon
Muraj, Hamza – Quiz 3 – Due: Apr 5 2006, 10:00 pm – Inst: Florin 2 9. Δ t = 3 8 v 0 μ g 10. Δ t = 1 4 v 0 μ g Explanation: From the perspective of the surface, let the speed of the center of the disk be v surface . Using the frictional force f , we can determine the acceleration X F s = m a , and f = μ m g , so a = μ g . Then v surface = v 0 - a t = v 0 - μ g t . (1) After pure rolling begins there is no longer any frictional force and consequently no longer any acceleration. From the perspective of the center of the disk, let the tangential velocity of the rim of the disk be v disk , the angular velocity be ω ; the angular acceleration is X τ = I α , so α = τ I = μ m g R 5 6 m R 2 = 6 5 μ g R . (2) The time dependence of ω is ω = α t = 6 5 μ g R t , so v disk R ω = 6 5 μ g t . (3) When the disk reaches pure rolling, the veloc- ity from the perspective of the surface will be
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 04/12/2010 for the course PHY 58195 taught by Professor Turner during the Spring '09 term at University of Texas at Austin.

Page1 / 14

quiz3 - Muraj, Hamza Quiz 3 Due: Apr 5 2006, 10:00 pm Inst:...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online