EF 151 Exam #3, Spring, 2014 Page 1 of 6

Transcription

1 EF 151 Exam #3, Spring, 2014 Page 1 of 6 Name: Section: Instructions: Put name and section on exam and on equation sheet. 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. 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 Include directions for all vectors

2 EF 151 Exam #3, Spring, 2014 Page 2 of 6 1. (2 pts) How was the actual final velocity determined in the roller coaster project (ball bearing in the tube)? A. Conservation of energy B. Conservation of momentum C. Projectile motion D. F = ma 2. (2 pts) Which is NOT a valid unit for work and energy? A. BTU B. Joule C. ft-lb D. kw-hr E. slug-ft 2 /s 2 F. slug-ft 3. (2 pts) A 20 lb box is pushed a distance of 5 ft along a level floor with a horizontal force of 10 lb. There is a constant friction force of 4 lb. How much work is done by the friction force? A ft-lb B. -50 ft-lb C. -20 ft-lb D. 0 E. 20 ft-lb F. 50 ft-lb G. 100 ft-lb 4. (2 pts) What is the value for the coefficient of restitution for a perfectly inelastic collision? A. 0 B. Between 0 and 1 C. 1 D. Greater than 1 E. Depends upon v1 and v2 5. (2 pts) A bowling ball (mass=30m, velocity=v) and billiard ball (mass=m, velocity= -v) collide in a head on, perfectly elastic collision. What is the closest value for the velocity of the billiard ball after the collision? A. - 3v B. - 2v C. - v D. 0 E. v F. 2v G. 3v

3 EF 151 Exam #3, Spring, 2014 Page 3 of 6 6. (2 pts) In a 2D indirect collision where e=0.5, in which direction do the velocity components change? A. Horizontal B. Vertical C. X D. Y E. Plane of Contact F. Line of Impact 7. (2 pts) What formula would you use to calculate the force required to compress a linear spring a given distance? A. F = kx B. U = ½kx 2 C. K = ½mv 2 D. F = ma E. Ft = mv 8. (2 pts) If a ball on a track is released from rest at the position shown, will it make it through the loop without leaving the track? A. Yes B. No C. Depends on the radius D. Depends on the friction 9. (2 pts) Assuming no losses, which coaster would have the greater speed at the bottom? A. Coaster 1 B. Coaster 2 C. Both will have the same speed D. Depends on the shape of the hill 10. (2 pts) What is the name of Jimmy Neutron s Dog? A. Lazydog B. Izzy C. Goddard D. Isaac E. Lassie F. Stan Goddard and Jimmy

4 EF 151 Exam #3, Spring, 2014 Page 4 of (16 pts) The Estabrook elevator has an electric motor that consumes 3.14 kw of electricity while raising the elevator and its occupants from the basement to the attic (40 ft height difference). The elevator weighs 500 lb and each of the 3 occupants weighs 160 lb. How long does the trip take if the elevator is 75% efficient? ( 1 W = ft-lb/sec) 12. (16 pts) A 2000 N roller coaster car at the bottom of a 30 m diameter circular loop is moving at 40 m/s. An engine on the coaster provides a constant net driving force of 400 N as it goes through the loop. What is the car s speed at the top of the loop? (neglect losses)

5 EF 151 Exam #3, Spring, 2014 Page 5 of (16 pts) A spring (k = 40 lb/ft) is used to shoot a box full of pies along a horizontal floor (µ k = 0.314) The spring is compressed with an 18 lb force and then it is released. The box slides a total distance of 21 ft (measured from the release point) before it stops. What is the weight of the box? (the box is not attached to the spring). 21 ft 14. (16 pts) A 140 g baseball is struck by a 1.00 kg baseball bat. Assume the ball is moving horizontally at 45 m/s while the bat moves horizontally at 31.4 m/s in the opposite direction. The coefficient of restitution between the two objects is What is the speed of the ball after it is struck?

6 EF 151 Exam #3, Spring, 2014 Page 6 of (16 pts) Two disks sliding on a frictionless surface are moving as shown. The disks have Velcro on their sides so they stick together. What is the velocity of the disks after the collision? (Hint: you do not need to work with the plane of contact/line of impact for this type of collision) 50 g 1.25 m/s 3.14 m/s g