This preview shows pages 1–2. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: Version PREVIEW hk 9 Opyrchal (11105) 1 This printout should have 14 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. Spin Dry Cycle 001 10.0 points The tub of a washer goes into its spindry cycle, starting from rest and reaching an an gular speed of 5 . 3 rev / s in 7 . 4 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 7 . 3 s . Through how many revolutions does the tub turn? Assume constant angular accelera tion while it is starting and stopping. Correct answer: 38 . 955 rev. Explanation: Let : = 0 rev / s , 1 = 5 . 3 rev / s , t 1 = 7 . 4 s , 2 = 0 rev / s , and t 2 = 7 . 3 s . = av t = i + f 2 t = 1 2 t in each case since either the initial or final speed is zero. While speeding up, 1 = 5 . 3 rev / s 2 (7 . 4 s) = 19 . 61 rev and while decelerating, 2 = 5 . 3 rev / s 2 (7 . 3 s) = 19 . 345 rev , so = 1 + 2 = 19 . 61 rev + 19 . 345 rev = 38 . 955 rev . Grinding Wheel Rotation 002 (part 1 of 2) 10.0 points A grinding wheel, initially at rest, is ro tated with constant angular acceleration of 7 . 04 rad / s 2 for 4 . 97 s. The wheel is then brought to rest with uniform deceleration in 14 . 9 rev. Find the angular deceleration required to bring the wheel to rest. Correct answer: 6 . 53825 rad / s 2 . Explanation: Let : = 0 rad / s , 1 = 7 . 04 rad / s 2 , t 1 = 4 . 97 s , and 2 = 14 . 9 rev . From kinematics f = + t. First find the speed attained before the wheel begins to slow down. Since = 0 rad / s for the acceleration, the final speed 1 = 1 t 1 for the acceleration is also the initial speed for the deceleration....
View
Full
Document
 Spring '12
 James
 Physics

Click to edit the document details