EF 151 Exam 4 Fall, 2017 Page 1 Copy 223

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1 EF 151 Exam 4 Fall, 017 Page 1 Copy 3 Name: Section: Before the Exam Starts: Sit in assigned seat; failure to sit in assigned seat results in a 0 for the exam. Put name and section on your exam. Put seating label on your equation sheet. Do not open the test until you are told to do so. Instructions and Guidelines for the Exam: On the first page, completely color in the dot for your chosen answers. Write your final answers in the boxes provided Assume 3 significant figures for all given numbers unless otherwise stated Show all of your work no work, no credit Include units for all answers and directions for all vectors At the end of the Exam: If you finish with less than 5 minutes remaining, please stay seated until the exam is over. Stop work immediately when time is over; working after time is over results in an automatic point deduction Turn in your equation sheet with your examination. Pass exams to the aisle; stay seated until all exams are collected. 8:10 9:40 11:10 1:40 :10 3: A10 Justin B10 Chris C10 Justin D10 Rekesh E10 Rekesh F10 Rekesh A1 Daniel B1 Daniel C1 Daniel A16 Andrea B16 Andrea C16 Andrea D16 Heather E16 Heather F16 Heather A17 Landon B17 Landon C17 Landon D17 Tayler E17 Tayler F17 Tayler A18 Matthew B18 Matthew C18 Matthew D18 Chris E18 Justin Hollow sphere Solid circular plate I mr 3 Solid cylinder I I z x 1 I z mr 1 mr 1 I y mr 4

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3 EF 151 Exam 4 Fall, 017 Page 3 Copy 3 Name: Section: 1. ( pt) Enter your EXAM ID from your seating label. If you don t know your exam ID, enter Digit #1 Digit # Digit #3 4. ( pt) Which is NOT an acceptable way to calculate angular momentum? r mv Iω r F r p 5. ( pt) What is NOT an acceptable way to calculate power? F v F ω τ ω W t 6. ( pt) A tennis ball, with radius r, is spun on a string of negligible mass with length L, as shown. The string is attached to the outside of the tennis ball. What is the appropriate equation for calculating the mass moment of inertia of this system? r L I = 3 mr I = 3 mr + mr I = 3 mr + ml I = 3 mr + m(r + L) 7. ( pt) Justin is standing on a rotating platform that is initially not rotating and is holding a spinning bicycle wheel that has an angular momentum of + kg-m /s k. Justin turns the bicycle wheel so that the wheel has an angular momentum of + kg-m /s j. What is Justin s angular momentum after he turns the bicycle wheel? 0 kg-m /s k + kg-m /s k +4 kg-m /s k - kg-m /s k -4 kg-m /s k 8. ( pt) The value of j j is: 0 i i j j k k 9. ( pt) A spinning object completes one revolution every 0.7 sec. What is the frequency of the object s rotation? 0.7 sec 1.43 sec 0.7 revolutions/sec 1.43 revolutions/sec

4 EF 151 Exam 4 Fall, 017 Page 4 Copy ( pt) An object is traveling in a circular path and its speed is increasing. Which is true? a normal = 0 a tangential = 0 a normal 0 a tangential = 0 a normal = 0 a tangential 0 a normal 0 a tangential ( pt) The FBD of an object that rotates about its center of mass is shown. Based on our standard coordinate system, the torque about the center of mass is: +T r T r T r W r T r + W r T r W 1. ( pt) A cylinder (I cm =.1 kg-m ) has a net torque (τ net = +7 N m) applied to it, causing it to rotate. What is the angular acceleration of the cylinder? rad s rad s rad s rad 1.85 s 13. (16 pts) The object below contains both a square and circular hole. Determine the radius of the circle if the x-coordinate of the center of mass is 1. in. Assume uniform thickness and density. 9 in 7.5 in r 5 in y x 5 in

5 EF 151 Exam 4 Fall, 017 Page 5 Copy (16 pts) A uniform, circular 0.9 ft diameter pulley has a wire wrapped around it and is connected to a weight (as shown). The other end of the wire is connected to a spring that is attached to the ground. The system starts from rest and starts with the spring in its undeformed position. What is the speed of the weight after the weight has dropped.7 ft? [Reminder F = kx and U e = 1 kx ] mwheel = 1.7 slugs lb 10 ft k = 3 lb/ft 15. (16 pts) A 160 lb person is skating with an increasing speed on a flat roller skating rink with a radius of 4.3 ft. The maximum speed the skater can go before they start sliding is 19.1 ft/s. What is the skater s tangential acceleration? A complete top view FBD=KD is required. [Coefficent of Friction for Skate Wheels: s = 0.6; k = 0.47] TOP VIEW FBD KD

6 EF 151 Exam 4 Fall, 017 Page 6 Copy (16 pts) A small pulley (r s = 13in) is driven by the belt connected to a motor. The small pulley is connected by a common axle to a larger pulley (r l = 18 in). The large pulley has a thin wire wrapped around it. The pulleys start from rest and after minutes, the belt driving the small pulley has a linear speed of 7 in/s. How much wire has been unwound in minutes? Motor small pulley large pulley wire 17. (16 pts) Determine the net torque about point A (counterclockwise is positive). 77 o 74 lb 135 lb.9 ft 36 o 1. ft 3 lb A 0.7 ft