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Unformatted text preview: al-ameri (aoa434) – Hwk09 – Stokes – (19102)1This print-out should have 25 questions.Multiple-choice questions may continue onthe next column or page – find all choicesbefore answering.This is Online Homework No9. It is duebefore 6.00 am on Tuesday 7 April, Abu DhabiTime (11.00 pm on Monday in Texas)001(part 1 of 2) 10.0 pointsA car accelerates uniformly from rest andreaches a speed of 15.2 m/s in 4.2 s. Thediameter of a tire is 51.2 cm.Find the number of revolutions the tiremakes during this motion, assuming no slip-ping.Correct answer: 19.8446 rev.Explanation:Let :vf= 15.2 m/s,r= 25.6 cm = 0.256 m,andt= 4.2 s.Sincevo= 0, the distance the car traveledduring the time interval iss= ¯v t=vo+vf2t=12vft,so from rolling without slipping,θ=sr=vft2r=(15.2 m/s) (4.2 s)2 (0.256 m)·1 rev2πrad=19.8446 rev.002(part 2 of 2) 10.0 pointsWhat is final rotational speed of a tire?Correct answer: 9.44982 rev/s.Explanation:The final angular velocity isω=Δvr=15.2 m/s.256 m·1 rev2πrad=9.44982 rev/s.keywords:00310.0 pointsThe tub of a washer goes into its spin-drycycle, starting from rest and reaching an an-gular speed of 7 rev/s in 8.7 s.At this pointthe person doing the laundry opens the lid,and a safety switch turns off the washer. Thetub slows to rest in 17.7 s.Through how many revolutions does thetub turn? Assume constant angular accelera-tion while it is starting and stopping.Correct answer: 92.4 rev.Explanation:Let :ω= 0 rev/s,ω1= 7 rev/s,Δt1= 8.7 s,ω2= 0 rev/s,andΔt2= 17.7 s.θ=ωavΔt=ωi+ωf2Δt=ω12Δtin each case since either the initial or finalspeed is zero. While speeding up,θ1=7 rev/s2(8.7 s) = 30.45 revand while decelerating,θ2=7 rev/s2(17.7 s) = 61.95 rev,soθ=θ1+θ2= 30.45 rev + 61.95 rev=92.4 rev.00410.0 pointsThe speed of a moving bullet can be deter-mined by allowing the bullet to pass throughtwo rotating paper disks mounted a distance85 cm apart on the same axle.From theangular displacement 27.5◦of the two bul-let holes in the disks and the rotational speed466 rev/min of the disks, we can determinethe speed of the bullet.al-ameri (aoa434) – Hwk09 – Stokes – (19102)227.5◦v466 rev/min85 cmWhat is the speed of the bullet?Correct answer: 86.4218 m/s.Explanation:Let :ω= 466 rev/min,d= 85 cm,andθ= 27.5◦.θ=ω tt=θω,so the speed of the bullet isv=dt=dωθ=(85 cm) (466 rev/min)27.5◦×360◦1 rev1 m100 cm1 min60 s=86.4218 m/s.keywords:005(part 1 of 3) 10.0 pointsAs a result of friction, the angular speed of awheel c hanges with time according todθdt=ωe−σ t,whereωandσare constants. The angularspeed changes from an initial angular speedof 5.27 rad/s to 3.97 rad/s in 3.92 s.Determine the magnitude of the angularacceleration after 1.64 s....
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