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Chapter Five Review By Jacqueline Lawrence,2014-12-04 10:02 558 views 0 Chapter Five Review
Chapter Five Review 7. What does the following series of energy pie charts tell you about the behavior of the object? Explain.
__ 1. A 2 kg mass is held 4 m above the ground. What is the approximate potential energy due to gravity of the mass with respect to the ground? a. 20 J. b. 40 J. c. 60 J. d. 80 J. e. none of these. __ 2. It takes 40 J to push a large box 4 m across a floor. Assuming that the push is in the same direction as the displacement, what is the size of the force on the box? For questions 8-9, make quantitative comparisons, by determining the ratio called a. 4 N. b. 10 N. for in the question. Show work or provide some argument c. 40 N. for your answer. d. 160 N.
e. none of these. 8. Two balls, A & B, of equal mass are released from rest __ 3. Which requires more energy: lifting a 50 kg sack vertically 2 meters or lifting a 25 kg at the heights indicated at left. sack vertically 4 meters? EgB a. Determine the value of the ratio Ea. lifting the 50 kg sack. gAb. lifting the 25 kg sack. c. both require the same amount of work. VB b. Determine the value of the ratio at impact. __ 4. A car moving at 15 m/s skids to a stop in 20m. If the car travels at 45 m/s, how far VAwill it skid, assuming the same constant braking force? a. 20 m.
b. 50 m. c. 90 m. 9. Consider the diagram at left which shows two d. 120 m. balls, A and B, which are dropped from the e. 180 m. same height. Ball B has twice the mass of ball __ 5. Suppose E is the energy transferred stretching a spring from 0 to 0.10 m. The A. amount of work done stretching the same spring from 0.10 m to 0.20 m is: EgBa. E a. Determine the value of the ratio Eb. 2E gAc. 3E d. 4E VB b. Determine the value of the ratio at VA__ 6. A crate is dragged across a floor at constant speed. The work done on the system can be accounted for by impact. a. E el b. E kc. How does the acceleration of B compare to c. E gthat of A? d. E diss e. both b and d
For questions 10-11 complete the energy bar graphs; be sure to define your system. 10. You pull a wagon, initially at rest, until it reaches constant velocity, along a level sidewalk.
13. How much kinetic energy does the car have at point C? Explain or calculate. 14. How fast is the car moving at point B? Show work. 11. A dart gun fires a dart straight up which then sticks to the ceiling.
15. Suppose the spring below has a spring constant of 50. N/m. The box has a mass of 8.0 kg and rests on a surface of negligible friction.
? For questions 12-14, consider the diagram representing a portion of an amusement park a. In the diagram at left, the spring was compressed 4.0 m. How much energy ride. A 100 kg car has 30,000 J of Potential Energy at point A. It moves down a does the spring now store? frictionless track and comes to a stop as it compresses a huge spring at point D.
b. Suppose that all the elastic energy were transferred to the box when it was released (diagram at right). How fast would the box be moving? 12. On the axes below, sketch the energy bar graphs when the car is at the indicated points.
16. A 7500 kg 18-wheeler traveling at 20 m/s exits onto the runaway truck ramp on the freeway. When it comes to a stop, it is 10 m higher than before. Complete the energy bar graph below. How much energy was dissipated by friction?
;17. Hulky and Bulky, two FedEx workers, decide to race each other up a flight of stairs (?h = 4.0 m) at the warehouse. Hulky, whose mass is 120 kg, makes the climb in 3.0 s; while Bulky, 150 kg, took 4.0 s to make the climb. a. Who has more E at the top? g b. Who exerted more power getting there?
MULTIPLE CHOICE 6. Which of the following is that form of energy associated with an object's motion? 1. The quantity of work equal to one joule is also equivalent to which of the following? a. potential b. thermal a. watt c. bio-chemical b. watt/s d. kinetic c. watt * s 2 d. watt/s 7. The rate at which work is done is equivalent to which of the following? 2. A 3 kg object starting at rest falls to the ground from a height of 1O m. Just before hitting the earth what will be a. increase in potential energy 2 its kinetic energy? (g = 9.8 m/s and assume air resistance is b. thermal energy negligible.) c. potential energy d. power a. 98 J b. 0.98 J 8. As an object is lowered into a deep hole in the surface of the c. 29.4 J earth, which of the following must be assumed in regard to its d. 294 J potential energy? 3. A 40 N crate is pulled 5 m up an inclined plane at a constant a. increase o velocity. If the plane is inclined at an angle of 37 to the b. decrease horizontal, what is the magnitude of the work done on the c. remain constant crate by the force of gravity? d. cannot tell from the information given a. 120 J 9. The unit of work, joule, is dimensionally the same as which of b. 6 J the following? c. 1180 J d. 200 J a. newton/second b. newton/kilogram 4. A 40 N crate is pulled up a 5 m inclined plane at a constant c. newton-second o velocity. If the plane is inclined at an angle of 37 to the d. newton-meter horizontal and there exists a constant force of friction of 10 N between the crate and the surface, what is the net gain in 10. A worker pushes a wheelbarrow with a horizontal force of 50 N potential energy by the crate in the process? over a distance of 5 m. What work does the man do? a. 120 J a. 10 J b. -120 J b. 1250 J c. 200 J c. 250 J d. -200 J d. 55 J 5. A 20 N crate starting at rest slides down a rough 3 m long 11. A worker pushes a 250 N weight wheelbarrow up a ramp 6.0 m in o ramp, inclined at 30 with the horizontal. The force of length and inclined at 20 with the horizontal. What friction between crate and ramp is 6 N. The crate, with the potential energy change does the wheelbarrow experience? mass of approximately 2 kg, will have what velocity at the bottom of the incline? a. 513 J b. 1500 J a. 0.5 m/s c. 3550 J b. 1.4 m/s d. 4500 J c. 2.8 m/s d. 3.4 m/s
12. A 1500 kg car travels along a highway at a speed of 20 m/s. 17. A baseball catcher puts on an exhibition by catching a 0.15 What is its kinetic energy? kg ball dropped from a helicopter at a height of 61 m. If the catcher "gives" with the ball for a distance of 0.75 m 5 a. 15.0 x 10 J while catching it, what average force is exerted on the mitt 52 b. 2.5 x 10 J ) by the ball? (g = 9.8 m/s5 c. 3.0 x 10 J 5 d. 6.0 x 10 J a. 47 N b. 94 N 13. A 15.0 kg crate, initially at rest, slides down a ramp 2.0 m c. 119 N long and inclined at an angle of 20 with the horizontal. If d. 376 N there is no friction between the ramp surface and crate, what is the velocity of the crate at the bottom of the ramp? 18. A simple pendulum, 2.0 m in length, is released with a push 2o (g = 9.8 m/s ) when the support string is at an angle of 25 from the vertical. If the initial speed of the suspended mass is 1.2 a. 6.1 m/s m/s when at the release point, what is its speed at the 2 b. 3.7 m/s bottom of the swing? (g = 9.8 m/s) c. 10.7 m/s d. 8.3 m/s a. 2.3 m/s b. 2.6 m/s 14. A pulley-cable system on a crate hoists a bucket of cement c. 2.0 m/s with a total weight of 20,000 N to a height of 40 m. If d. 0.5 m/s this is accomplished in 2 min., what is the power output by the pulley-cable system? 19. An automobile delivers 30 hp to its wheels when moving at a constant speed of 22 m/s. What is the resistance force on a. 6.7 kW the automobile at this speed? (1 hp = 746 watts) b. 3.3 kW 3 c. 13.3 kW a. 18.6 x 10 N 5 d. 400 kW b. 4.1 x 10 N c. 1020 N d. 848 N 15. A horizontal force of 200 N is applied to move a 55 kg cart across a 10 m level surface. What work is done by the 200 N force? 20. The work done by static friction is always a. 4000 J a. positive b. 5400 J b. negative c. 2000 J c. along the surface d. 2700 J d. zero 16. A horizontal force of 200 N is applied to a 55 kg cart 21. A ball hits a wall and bounces back at half the original across a 10 m level surface. If the cart accelerates at 2.0 speed. What part of the original kinetic energy of the ball 2 m/s then what force of friction acts to retard the motion did it lose in the collision? of the cart? a. 1/4 a. 110 N b. 1/2 b. 90 N c. 3/4 c. 80 N d. it did not lose kinetic energy. d. 70 N
522. A 2 kg ball which originally has zero kinetic and potential 27. A jet engine develops 10 N of thrust in moving an airplane energy is dropped into a well which is 10 m deep. Just forward at a speed of 900 km/hr. What is the power before the ball hits the bottom, the sum of its kinetic and developed by the engine? potential energy is a. 5 MW a. 0 b. 10 MW b. 196 J c. 25 MW c. -196 J d. 50 MW d. 392 J 28. A pole vaulter clears 6 m. With what velocity does he 23. Two blocks are released from the top of a building. One strike the mat in the landing area? falls straight down while the other slides down a smooth ramp. If all friction is ignored, which one is moving faster a. 2.7 m/s when it reaches the bottom? b. 5.4 m/s c. 10.8 m/s a. The block that went straight down. d. 21.6 m/s b. The block that went down the ramp. c. They both will have the same speed. 29. Water flows over a section of Niagara Falls at a rate of 6 d. Insufficient information to work the problem. 1.2 x 10 kg/s and falls 50 m. What is the power generated by the waterfall? 24. A girl and her bicycle have a total mass of 40 kg. At the top of the hill her speed is 5 m/s. The hill is 10 m high a. 588 MW and 100m long (down the incline). If the force of friction b. 294 MW as she rides down the hill is 20 N, what is her speed at the c. 147 MW bottom? d. 60 MW a. 5 m/s 30. A bobsled makes a run down an ice track starting at 150 m b. 10 m/s vertical distance up the hill. If there is no friction, what c. 11 m/s is the velocity at the bottom of the hill? d. She stops before she reaches the bottom. a. 27 m/s b. 36 m/s 25. An 80,000 kg airliner is flying at 900 kilometers/hour at a height of 10 kilometers. What is its total energy (kinetic + c. 45 m/s potential)? d. 54 m/s ANSWER KEY a. 2500 MJ b. 4780 MJ c. 7730 MJ 1. c 11. a 21. c d. 10340 MJ 2. d 12. c 22. a 3. a 13. b 23. c 26. A 60 g golfball is dropped from a height of 2 m and rebounds 4. a 14. a 24. c to 1.5 m. How much energy is lost? 5. d 15. c 25. d 6. d 16. b 26. a a. 0.29 J 7. d 17. c 27. c b. 0.5 J 8. b 18. a 28. c c. 0.88 J 9. d 19. c 29. a d. 1 J 10. c 20. d 30. d
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