Review for Final Exam CP Physics E. Burns

Dwight Englewood Summer Program Physics For Advancement

Answers to Multiple Choice (Answers highlighted)

1. Which person has the greatest inertia? a. A 110-kg wrestler resting on a mat. b. A 90-kg man walking at 2 m/s. c. A 70-kg man running at 5 m/s. d. A 50-kg girl sprinting at 8 m/s

2. Two equal-mass safety dummies are being used to test seat belts. Dummy A has a wide seat belt and Dummy B has a narrow seat belt. Both dummies are crashed into a barrier while in the same car. Which statement below best describes the forces needed to stop each dummy? a. Dummy A’s force is bigger than Dummy B’s. b. Dummy B’s force is bigger than Dummy A’s. c. The forces on the two dummies are equal d. The forces cannot be determined unless you know the exact size of the seatbelts.

3. When a rapidly descending elevator is quickly stopped, blood tends to drain away from the head of a rider in the elevator. The principle that best describes this phenomenon is a. Objects at rest tend to remain at rest. b. Pressure varies with area and the applied force. c. For every action there is an equal and opposite reaction. d. Objects in motion tend to continue in motion with constant speed. e. Force is directly proportional to acceleration.

4. In a demonstration, a student throws a raw egg at a bed sheet held by 2 other students and the egg does not break. The best reason to explain why the egg does not break is that… a. The sheet is made of soft cotton. b. The student threw the egg at an angle so it struck the sheet at a glancing blow. c. The sheet stops the egg over a large distance, leading to a small force. d. The egg landed on its end, which is harder to break.

5. A 50-kg girl is running along a track at 4 m/s. What is the girl’s kinetic energy? a. 200 J b. 400 J c. 800 J d. 650 J

6. A 1.0 kg cart traveling at a constant 2.0 m/s across a level lab table 0.80 m above the floor is stopped in a distance of 0.20 m. The amount of work required to stop the cart is a. 1 J b. 2 J c. 2.5 J d. 4 J 7. In Question 6, if the cart stopped in half the distance, the force required to stop the cart would be a. Half as great b. The same c. Twice as great d. Four times as great

8. In Question 6, if the cart stopped in half the distance, the amount of work required to stop it would be a. Half as great b. The same c. Twice as great d. Four times as great

9. You are a passenger in a car stopped at a red light. If your car was to get rear ended by another car behind you, which way would your head move, relative to the car? a. Forwards b. Backwards c. Sideways towards the driver. d. Sideways towards the window

10. In which of the diagrams below does the block have a net external force acting on it? 5N 5N 15N A. B. 15N

5N 15N

5N 5N 15N 5N C. D.

15N 15N

11. If all the forces on a block are balanced, then the block cannot be a. At rest. b. Moving with constant speed to the right. c. Moving with constant speed to the left. d. Accelerating.

12. The diagram at right shows a collision between 2 carts of equal mass. Cart A has a spring on the front and is moving forward, while cart B is at rest. After cart A hits cart B, which of the following will occur?

a. Cart A stops and cart B moves forward. b. Cart A continues forward with the same speed as cart B. c. Cart A bounces backward and cart B stays at rest. d. Cart A bounces backward and cart B moves forward. 13. In Question 12, cart B now has a mass double that of cart A when the collision occurs. After cart A hits cart B, which of the following will occur? a. Cart A stops and cart B moves forward. b. Cart A continues forward with the same speed as cart B. c. Cart A bounces backward and cart B stays at rest. d. Cart A bounces backward and cart B moves forward.

14. A student does an experiment to check the mass of a cart. The student sends a 1.0 kg cart with a spring attached at the front end into a collision with a cart of unknown mass. After the collision, the student notes that the 1.0 kg cart moves forward with reduced speed, and the unknown cart moves forward at a faster speed than the 1.0 kg cart. What does this experiment show about the mass of the unknown cart? a. The unknown cart is more than 1.0 kg. b. The unknown cart is less than 1.0 kg. c. The unknown cart is equal to 1.0 kg. d. No information about the mass of the unknown cart can be obtained from this experiment.

15. A 2.0 kg cart moving with a speed of 3 m/s collides with a 1.0 kg cart that is at rest. After the collision, the two carts stick together. What is the velocity of the combined mass of the two carts after the collision? a. 1.0 m/s b. 2.0 m/s c. 3.0 m/s d. 1.5 m/s

16. A 2.0 kg cart and a 1.0 kg cart at rest on a level surface with a compressed spring between them as shown. When the spring is released, if the 1.0 kg cart moves off with a speed of 3.0 m/s, what is the speed of the 2.0 kg cart?

a. 1.0 m/s b. 2.0 m/s c. 3.0 m/s d. 1.5 m/s

17. A 8500-kg truck moving rightward with a speed of 12 m/s collides head on with a 1200-kg car moving to the left at 25 m/s. The car moves with a velocity of 5 m/s to the right after the collision. Determine the post- collision velocity of the truck. 7.76 m/s 18. Three groups of students are testing their designs for cushioning collisions and obtain the force vs. time graphs shown below. If the areas under all three graphs are equal, which group’s design worked best at cushioning the collision?

a. Group A b. Group B c. Group C d. All three groups are equal.

19. In Question 18, which group’s cart had the greatest change in momentum when the three carts struck the force probe? a. Group A b. Group B c. Group C d. All three groups are equal.

20. In a car collision, a 44-kg passenger moving at 15 m/s is brought to rest by an air bag in 0.10 s. What is the average force the air bag exerts on the passenger? a. 440 N b. 4400 N c. 660 N d. 6600 N

21. A steel ball rolls across a level track a distance of 1.35 meters in a time of 0.45 seconds. What is the velocity of the ball? a. 0.33 m/s b. 1.80 m/s c. 3.0 m/s d. 0.61 m/s

22. A student does an experiment rolling a cart down a ramp. The cart starts from rest at the top of the ramp, and 1.5 s later the cart has a velocity of 2.0 m/s. What is the cart’s acceleration? a. 1.2 m/s2 b. 1.3 m/s2 c. 3.0 m/s2 d. 4.5 m/s2 23. A ball is moving 5 m/s east. After being struck by a bat, the ball is moving 7 m/s west. What is the change in velocity? a. -2 m/s b. +2 m/s c. -12 m/s d. +12 m/s

24. A ramp 1.2 m long rests on a level table with one end elevated 0.40 m above the table surface. A steel ball starts at the elevated end of the ramp and rolls down the ramp through a photogate. If the ball has a mass of 0.045 kg, what is the ball’s potential energy at the top of the ramp? a. 0.18 J b. 0.45 J c. 0.54 J d. 12 J

25. In the diagram, a 1.0 kg sphere at point A has a potential energy of 5.0 J. What is the potential energy of the sphere at point B, halfway down the plane? a. 0.0 J b. 3.0 J c. 2.5 J d. 5.0 J

Complete the table below for a 0.2-kg pendulum starting from rest at a height of 0.25 m. Your answer choices for each box are: (a) 0 J (b) 0.123 J (c) 0.245 J (d) 0.49 J Position of Pendulum Bob GPE (J) KE (J) GPE + KE (J)

Top (0.25 m) 26. d 27. a 28. d

Bottom (0 m) 29. a 30. d 31. d

Halfway down (0.125 m) 32. c 33. c 34. d

35. A spring has a spring constant of 120 N/m. How much potential energy is stored in the spring as it is stretched 0.20 m? a. 2.4 J b. 12 J c. 4.8 J d. 24 J 36. In the diagram, a student compressed the spring in a 0.01-kg pop-up toy a distance of 0.020 m. If 0.068 J of energy are stored in the toy, what is the toy’s spring constant?

a. 120 N/m b. 170 N/m c. 225 N/m d. 340 N/m

37. In question 36, how much kinetic energy would the spring toy have immediately after “popping”? a. 0.068 J b. 0.340 J c. 0.124 J d. 1.24 J

38. In Question 36, how high is the pop-up toy at the peak of its rise? a. 0.85 m b. 0.68 m c. 0.54 m d. 0.15 m

39. Two bodies attract one another with a gravitational force of 10.0 N. What will be the force of attraction if the mass of each body is doubled? a. 2.5 N b. 5.0 N c. 20 N d. 40 N

40. If the distance between two masses is tripled, the gravitational force between them would be a. 1/9 as great. b. 1/3 as great c. 3 times as great. d. 9 times as great.

41. A mass is rotating clockwise in a horizontal circle as shown in the diagram to the right. If the string breaks when the object is at point X, which arrow below best represents the path of the object after the string has broken?

A 42. A 50-kg student riding in the coaster car is sitting on a bathroom scale when the car is moving in a vertical circle, at the bottom of the loop. The circle has a radius of 8 m, and the car’s velocity at point A is 10 m/s. What would be the reading on the bathroom scale when the student and car are at the top of the loop? a. 0 N b. 135 N c. 500 N d. 625 N

43. A motor has a power output of 1000 W. Using this power, how much time will it take the motor to raise a 50-N weight 100-m? a. 5 s b. 10 s c. 50 s d. 100 s 44. To lift a roller-coaster car from rest at the bottom to rest at the top of the first hill, a force of 560 N acting parallel to hill is used. If the length of the incline is 80 m, what is the car’s increase in gravitational potential energy? a. 7 J b. 5600 J c. 44,800 J d. 450,000 J

45. A student who weighs 560 N climbs a flight of stairs that is 4 m high in 8 s. How much power does the student need to do this? a. 280 W b. 1120 W c. 5600 W d. 17,920 W

46. Which of the following statements explains why a heavy object falls at the same rate as a light object near the earth’s surface (neglecting air resistance). a. The force of gravity on the heavy object is more that that on the lighter one. b. The force of gravity is the same on both objects. c. The acceleration due to gravity is a higher value on the heavier object. d. None of the above, heavier objects do fall faster.

47. What provides the centripetal force that keeps the moon in orbit around the earth? a. normal force b. weight c. tension force d. magnetic force

48. Kepler's three laws of planetary motion are described below, EXCEPT for which one? a. The center of the sun is located at one focus of the elliptically-shaped path of the planets about the sun. b. The proportionality constant in the law of universal gravitation is equal to 6.67 x 10-11 Nm2/kg2 c. An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. d. The ratio of the cubes of the average distances of any two planets from the sun is equal to the ratio of the squares of the periods.

49. What was wrong with Kepler's laws? a. The laws were not based on concrete data. b. Nothing, they provided a suitable framework for understanding the motion and paths of planets about the sun. c. There was no accepted explanation for why such paths existed or for the cause for how the planets moved as they did. d. The laws were incorrect and later proven wrong.

50. If the separation distance between two objects is increased by a factor of 2, then the force of gravity is: a. decreased by a factor of two. b. Increased by a factor of two c. Decreased by a factor of four d. Decreased by a factor of four e. None of these, there is no relationship. 51. Suppose that two objects attract each other with a force of 16 units. If the distance between the two objects is halved, what is the new force of attraction between the two objects? a. 64 units b. 32 units c. 16 units d. 8 units e. 4 units

53. If you wanted to make a profit in buying gold by weight at one altitude and selling it at another altitude for the same price per weight, should you buy or sell at the higher altitude location? a. buy b. sell

54. Newton’s Law of Universal Gravitation was a breakthrough because it states that a. the force of gravity must be independent of the mass of the planet. b. the force of gravity must be inversely proportional to the mass of the object. c. the force of gravity must be directly proportional to the square of the distance which separates the centers of the two objects. d. ALL objects attract each other with a force of gravitational attraction.

55. True or False: More massive objects will attract each other with a greater gravitational force.

56. If the mass of one of the objects is doubled, then the force of gravity between them is a. Quartered b. halved c. unchanged d. doubled e. quadrupled

57. If a car stops at a red light immediately after throwing an apple core vertically out of the sunroof, where will the core land with respect to the car? Ignore air resistance. a. In front of the car. b. Back through the sunroof. c. Behind the car.

58. The curve below represents the path of a projectile near Earth’s surface. Point B is at the highest point along the projectile’s path. Points A and C are at the same height above the ground. Assume that the ground is level, and there is no air friction. Select the true statement about the projectile at point B. a. The acceleration of the projectile is zero B b. The velocity of the projectile is zero c. The x component of the projectile’s velocity is zero A C d. The y component of the projectile’s velocity is zero

59. Refer to the figure in the previous problem. Which of the following quantities are the same at both points A and C? a. The magnitude of the x component of the projectile’s velocity b. The magnitude of the y component of the projectile’s velocity c. The projectile’s acceleration d. All of the above.

60. An example of a vector quantity is which of the following? a. Velocity b. Temperature c. Volume d. mass

61. A student adds two vectors with magnitudes of 200 and 40. Of the following, which one is the only possible choice for the magnitude of the resultant? a. 100 b. 200 c. 260 d. 40 62. How much power does a machine that moves a crate weighing 100 N a distance of 5 meters in 10 seconds use? A) 0.5 W b.50 W c) 200 W d) 5000 W

63. Suppose a hill is 200 feet long, and quite steep. If you ride your bicycle up the hill along a zigzag path which is 800 feet long, the average force you must exert is: a. 4 times the average force you would exert going straight up. b. ¼ of the average force you would exert going straight up. c. ½ of the average force you would exert going straight up. d. equal to the average force you would exert going straight up. e. can’t tell the relationship to the average force you would exert going straight up.

64. For an object in circular motion, which of the following is true? a. Radial forces are responsible for change in the speed of the object b. Radial forces are responsible for the tangential motion. c. Radial forces are equal to zero. d. Radial forces are responsible for change in direction. e. Radial forces are not present in the situation described.

65. Which one of the following will not affect the speed at which a car could safely be driven around a flat circular track? a. Radius of the car b. Mass of the track c. Coefficient of friction between car and track d. All of the above do affect the speed

66. If the radius of an object in circular motion doubles, while all other variables stay the same, which of the following describes the net force on the object? a. doubles (x 2) b. quadruples (x 4) c. no change d. halves (x 0.5)

67. Neglecting air resistance, a stone falling from the roof of a single story building to the surface of the earth a. reaches its maximum speed quite soon after release and then falls at a constant speed thereafter. b. speeds up as it falls, primarily because the closer the stone gets to the earth, the stronger the gravitational attraction. c. speeds up because of the constant gravitational force acting on it. d. falls because of the intrinsic tendency of all objects to fall toward the earth. e. falls because of a combination of the force of gravity and the air pressure pushing it downward.

68. A dog stands on a scale in an elevator. The dog at rest weighs 60 N. The elevator accelerates upwards with an acceleration of 5 m/s2. The reading on the scale will be: a. 30 N b. 50 N c. 60 N d. 90 N e. 45 N

69. If a car is traveling north on a straight road and its brakes are applied, it will a. Have no acceleration b. Accelerate to the south c. Accelerate to the north. d. Accelerate either east or west e. Maintain a constant acceleration.

70. A ball projected up an inclined plane at point A reaches a maximum distance at point B, and then rolls back down the plane. The direction of the acceleration of the ball at point B is a. up the plane. B b. down the plane. c. zero. d. can not be determined. A e. none of the above.

71. A graph is plotted showing the velocity of a car as a function of time. If the graph is a straight, diagonal line, it means that a. The car started at rest b. Acceleration is constant c. Acceleration is increasing d. Velocity is constant e. Velocity is increasing

72. What does the shaded area under the line tell you about the motion of the moving object? a. The area is the velocity. b. The area is the distance traveled. c. The area is the speed. d. The area is the acceleration.

73. Which of the following distance vs. time graphs represents constant acceleration? a. b. c. d. d e. d d time t