EF 151 Exam #2 - Fall, 2014 Page 1 of 6

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1 EF 151 Exam #2 - Fall, 2014 Page 1 of 6 Name: Section: Instructions: Put your name and section on the exam. Do not open the test until you are told to do so. Write your final answer in the box provided If you finish with less than 5 minutes remaining, please stay seated until the exam is over. Stop work immediately when time is over; pass exams to the aisle; stay seated until all exams are collected. Working after time is over results in an automatic 10 point deduction. Turn in your equation sheet with your examination Guidelines: 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 8: :10 12:40 2:10 3: Front B S1a Daniel S2a Daniel S3a Tyler S4a Daniel S5a Tyler S6a Tyler a c C 111 Back S1b Andrew S2b Andrew S3b Andrew S4b Brandi S5b Brandi S6b Brandi Est 209 b A S1c Rachel S2c Rachel S3c Rachel S4c Jason S5c Jason S6c Jason Est 201 S1d Tayler S2d Tayler S3d Tayler S4d Sarah S5d Sarah S6d Sarah

2 EF 151 Exam #2 - Fall, 2014 Page 2 of 6 1. (2 pts) A baseball is rolled off a 3 ft high table. Just as the ball rolls off the table, a second baseball is dropped from the same height. Which baseball hits the ground first? Neglect air resistance. A. the baseball rolled off the table B. the baseball that was dropped C. both hit at the same time D. cannot determine which hits first 2. (2 pts) Timothy kicks a soccer ball at 20 m/s at an angle of 35 above the ground. The minimum speed while the ball is in the air is: A. 0 B. 20cos(35 ) m/s C. 20sin(35 ) m/s D. 20tan(35 ) m/s E. 20 m/s 3. (2 pts) Tayler is walking at a velocity of +6 ft/s on a moving sidewalk that is going at +2 ft/s. Rachel is walking alongside the sidewalk at a velocity of +5 ft/s. The velocity of Rachel with respect to Tayler is: A. -3 ft/s B. -1 ft/s C. +1 ft/s D. +3 ft/s 4. (2 pts) Andrew has an acceleration with respect to the ground of (4i + 6j)ft/s 2. Daniel has an acceleration with respect to the ground of (3i 2j)ft/s 2. The acceleration of Daniel with respect to Andrew is: A. (1i + 8j)ft/s 2 B. (-1i 8j)ft/s 2 C. (7i + 4j)ft/s 2 D. (-32.2j)ft/s 2 5. (2 pts) A cart is being pushed as shown. Neglect friction and air resistance. The acceleration of the cart is: A. 0.5 ft/s 2 B. 2.0 ft/s 2 C ft/s 2 D ft/s 2 6 lb 12 lb

3 EF 151 Exam #2 - Fall, 2014 Page 3 of 6 6. (2 pts) The correct FBD for a person sitting in a car that is moving to the left and slowing down is: A B C D E F 7. (2 pts) The static coefficient of friction between two objects is 0.8. Which value is not possible for the coefficient of kinetic friction between the two objects? A. 0.3 B. 0.5 C. 0.7 D (2 pts) What is the friction force between the box and the ground? A. 12 lb B. 18 lb C. 20 lb D. 30 lb 20 lb 30 lb μ s = 0.6, μ k = (2 pts) The terminal velocity of an object of mass M is V. What would the terminal velocity of an object of mass 2M be? (same size and shape) A. 2V B. 2V C. V 1 D. E. V 2 1 V (2 pts) Donnie Tyndall throws a basketball straight down. Considering air resistance, the acceleration of the basketball the instant after release is: A. greater than gravity B. equal to gravity C. less than gravity D. cannot determine

4 EF 151 Exam #2 - Fall, 2014 Page 4 of (16 pts) A water balloon is thrown out a window with an unknown speed at the angle shown. The balloon hits the ground 0.6 seconds after being thrown. How high is the window above the ground? (assume ideal projectile motion) y 15 v Hits ground 0.6 seconds after release 21 ft 12. (16 pts) Professor Schleter is driving his 20 kn minivan down a 1.4 degree incline. The drive (traction) force is 1200 N and there is significant air resistance. Determine the instantaneous acceleration when the van is traveling at 22 m/s. (FBD=KD required) F D = 1 2 ρac Dv 2 A = 2.9 m 2 ρ = 1.2 kg/m 3 C d = 0.35

5 EF 151 Exam #2 - Fall, 2014 Page 5 of (16 pts) Two 3000 lb tractors are working together to move a 2000 lb crate. The traction force of each tractor is 1200 lb to the right. The crate is sliding and experiences a friction force of 1400 lb. Determine the force in the connection (coupling) between tractor A and the crate. (2 FBD = KD required) Tractor B Crate Tractor A 14. (16 pts) An airplane is flying at a speed of 250 mph 30 E of N with respect to the ground and 230 mph 22.7 E of N with respect to the air. What is the speed of the wind?

6 EF 151 Exam #2 - Fall, 2014 Page 6 of (16 pts) Brandi is pushing on a box with a force of 30 lbs. What is the minimum force P that Sarah needs to pull on the box to get it to move? (FBD required) 30 lb 120 lb P 20 µs = 0.70, µk = 0.50