Buggé: Final Exam Review Problems 2011

Physics Final Exam Review 2011 *Note: these problems are a general overview of what we have learned. Going through your notes, textbooks, old quizzes, old tests, and possibly even some labs will aide in your studying for the final exam*

Kinematics Make sure you know how to: a) Draw a motion diagram for a moving object b) Determine the direction of acceleration using a motion diagram 1. Are you moving while sitting on a train that is leaving the station? 2. Describe the point-like model of a real object. Explain why we can use this model to describe the motion of a real object. 3. What information about a moving object can we extract from a motion diagram? 4. What is the difference between initial position, final position, distance, displacement, and path length? 5.

6. The position-vs-time graph for a moving object is a straight line with a slope equal to -15.0 m/s. Explain what this means about the motion of the object. 7. Give an example in which an object with negative acceleration and is speeding up. Give an example in which an object with positive acceleration is slowing down. 8. A car’s motion with respect to the ground is described by the following function: X(t) = (-48 m) + (12 m/s)t + (-2 m/s2)t2 Determine the car’s position and velocity at time zero. Also, determine its acceleration. At what time (if any) does the car’s velocity become zero? 9. How do you decide if you should use a positive or negative sign for the acceleration of an object moving in a vertical direction? 10. Why is “following too closely” not a very good explanation for why a tailgating accident occurs?

Buggé: Final Exam Review Problems 2011

11. While driving along a flat stretch on the highway, there is a policeman parked behind a bush. As you drive by he uses his speed gun to track your speed over a period of 10 seconds. The data he includes in his report is given in the table below. Time (s) 0 2 4 6 8 10

Velocity (mph) 45 60 78 94 108 125

a) b) c) d) e)

Plot a velocity vs time graph. What type of relationship is displayed on the graph? What is the equation of the graph? Using the graph, determine the displacement of your car after 8 seconds. Plot an acceleration vs time graph.

12. A turtle crawls at 10 cm/s. How long will it take the turtle to go 2 m? 13. If you throw a tennis ball straight up in the air with a velocity of 30m/s, how long will it take to come back to the ground? What is the acceleration of the ball when at the tippy-top of the flight? 14. Ashleigh and Rachael are bored with attending choral lessons inside the high school and decide instead to practice their singing while skydiving. They pick their new favorite song, Ring of Fire by Johnny Cash, and get into the airplane. Ignore air resistance. a) Sketch the situation b) Draw a motion diagram c) If Ring of Fire is 2 min 36 sec long, at what altitude do they have to fall from in order to finish the song right before reaching the ground? d) What will their final velocity be right before reaching ground? 15. Katie and Cassidy are at a cheerleading competition. In warm-ups, the team is testing how high they can throw each other. Cassidy is thrown upward first with an initial velocity of 25 ft/s. a) Sketch the situation b) How high does Cassidy go? c) How long is she in the air? d) What is her velocity right before her teammates catch her? 16. Kelsey is playing in a lacrosse game against South’s rival North. She catches a pass and has a breakaway against the goalie. Her initial speed is 2 m/s and she accelerates at a rate of 4 m/s2 for 3.4 s until she shoots the ball. a) Sketch the situation b) Draw a motion diagram c) How fast is she going when she releases the ball? d) How far did she run while accelerating?

Buggé: Final Exam Review Problems 2011

Forces and Newton’s Laws Make sure you know how to: a) Identify a system, construct a force diagram for it, and use the force diagram to apply Newton’s second law. 17. You slide toward the right at decreasing speed on a horizontal wooden floor. Choose yourself as the system and list external objects that interact with and exert forces on you. 18. A book bag is partially supported while hanging from a spring scale and also sitting on a platform scale. The platform scale reads about 36 units of force and the spring scale reads about 28 units of force. What is the magnitude of the force that Earth exerts on the bag? 19. Why do you need to keep pushing a grocery cart in a store in order to keep it moving? 20. An elevator in a tall office building moves downward at constant speed. How does the magnitude of the upward force exerted by the cable on the elevator compare to the magnitude of the downward force exerted by Earth on the elevator? Explain your reasoning. 21. What is the main difference between inertial and non-inertial reference frames? Give an example. 22. Jim says that ma is a special force exerted on an object and should be represented on the force diagram. Do you agree or disagree with Jim? Explain your answer. 23. Three friends are arguing about the type of information a bathroom scale reports. Eugenia says that it reads the weight of a person, Alan says that it reads the sum of the forces exerted on the person by Earth and the scale, and Mike says that the scale reads the force that the scale exerts on the person. Who do you think is correct? Why? 24. Identify third law force pairs for the following interactions: A rollerblader and the floor, a volleyball player and the volleyball, and a speeding up car’s tires and the road. 25. Explain how an airbag reduces the stopping force exerted on the driver of a car. 26. Draw all of the forces for the following rocks. no acceleration moving at constant speed moving in a circle around post

Buggé: Final Exam Review Problems 2011

27. It snowed early this year! You go outside over the Thanksgiving holiday and pull your 20-kg sled with an unbalanced horizontal force of 30 N across the ground a hill. a. Sketch the situation, circle the object of interest b. Solve for the acceleration of the sled. c. Draw and label a free body diagram for the object of interest d. Solve for any of the forces that you can in the FBD 28. Alex’s car (900 kg) stalls 10 m from the Amwell Road parking lot. Alex gets two of his strong physics friends, Sam and Tim, to help him move the car. The 3 students push horizontally with a force of 500 N each. a. Sketch the situation, circle the object of interest b. Draw and label a Free Body Diagram for the object of interest c. Solve for any of the forces that you can in the FBD d. What is the acceleration of the car? e. How long does it take them to reach the parking lot? 29. Sam (mass 68 kg) sees Santa’s sleigh (mass 400 kg) and jumps in. Rudolph is startled, and the reindeer start to pull the sled with a horizontal force of 1000 N. a. Sketch the situation, circle the object of interest b. Draw a free body diagram c. What is the acceleration of the sled? d. After 5 seconds the reins break, as Rudolph’s pulling is too strong. How far will the sled go before it comes to a stop if the frictional force of the snow on the sled is 150 N? e. What is the coefficient of kinetic friction ( µk ) between the slow and the sled?

Two Dimensional Motion ! 30. How can we represent the horizontal position as a function of time of an object launched out of a cannon? How can we represent the vertical position as a function of time of an object launched out of a cannon? 31. Michelle stands on the Millstone River Bridge kicking stones into the water below. A) If Michelle kicks a stone with a horizontal velocity of 3.50 m/s, and it lands in the water with a horizontal distance of 5.40 m from where Michelle is standing, what is the height of the bridge? B) If the stone had been kicked harder, how would this affect the time it would take to fall? 32. Jake drops a cherry pit out the car window 1.0 m above the ground while traveling down the road at 18 m/s. a) How far, horizontally, from the initial dropping point will the pit hit the ground? B) Draw a picture of the situation. C) if the car continues to travel at the same speed, where will the car be in relation to the pit when it lands?

Buggé: Final Exam Review Problems 2011

Circular Motion Make sure you know how to: a) Find the direction of acceleration using a motion diagram b) Draw a force diagram 33. How do we know that during constant speed circular motion, an object’s acceleration, a, points toward the center of the circle? 34.

35. Use your understanding of Newton’s laws to explain why you tend to slide across the car seat when the car makes a sharp turn? 36. A 13 g holiday ornament is attached to a 0.93 m string. The stopper is swung in a horizontal circle making one revolution in 1.18 s. Determine the force exerted by the string on the stopper. 37. A carnival clown rides a motorcycle down a ramp and around a vertical loop. If the loop has a radius of 18 m, what is the slowest speed the rider can have at the top of the loop (where he feels weightless) to avoid falling?

Static Equilibrium 38. A 1 m long 10 kg shelf is attached to the wall by a hinge so it can collapse and hide away. When you need it you can hang it by the other end with a chain from the ceiling. Currently, the shelf is holding 5 kg worth of books 0.6 m away from the wall, a pair of 2kg glasses 0.9 m away from the wall, and your 12 kg laptop 0.3 m away from the wall. The maximum force of tension that the chain can withstand before breaking is 120 N. a) Will it be able to support all of these objects? b) What is the force of tension in the chain? c) If it cannot support the objects, what can we do to provide additional support for the shelf?

Buggé: Final Exam Review Problems 2011

39. A meter stick (100 cm) is supported at the 50 cm mark. A 20 g mass sits on the 20 cm mark, a 40 g mass sits on the 40 cm mark, a 60 g mass sits on the 60 cm mark, and an 80 g mass sits on the 80 cm mark. Where would a 150 g mass need to be located in order to balance the system? (cm) 40. Fred (95kg) sits 1.25 meters away from the middle of a seesaw. How far away should another person (75kg) sit in order to balance out the see saw?

Impulse and Momentum Make sure you know how to: a) construct a force diagram for an object b) use kinematics to describe an object’s motion c) use bar charts d) understand the difference between constant and conserved for various systems 41. Give an everyday example of a situation and a choice of system where the mass of the system is constant but some other physical quantity is not. 42. Two identical cars are traveling toward each other at the same speed. One of the carts has a piece of modeling clay on its front. The carts collide, stick together, and stop; the momentum of each cart is now zero. If the system includes both carts, did the momentum of the system disappear? Explain your answer. 43. An apple is falling from a tree. Why does its momentum change? Specify the external force responsible. Find a system in which the momentum is constant during this process. 44. Why can you draw bar charts that have zero external impulse, or for the same process non-zero external impulses? Why can the bar charts differ? 45. As a bullet enters a block, the block exerts a force on the bullet, causing the bullet’s speed to decrease to almost zero. Why can we use the idea of momentum constancy to analyze this situation? 46. When a meteorite hits the Earth, the meteorite’s motion apparently disappears completely. How can we claim that momentum is conserved? 47. Robin Hood has a mass of 35kg and shoots a 0.1kg arrow at a speed of 150m/s, causing him to move in the opposite direction. a. Sketch the before and after situations b. Construct an impulse-momentum bar chart c. What is the recoil speed of the archer? 48. A 0.3-kg tennis ball traveling at 15 m/s is returned by Daria. It leaves her racket with a speed of 44 m/s in the opposite direction from which it came. a. Sketch the situation. b. Construct an impulse-momentum bar chart c. If the racket and the ball are in contact for 0.05 s, calculate the average force the racket exerts on the ball.

Buggé: Final Exam Review Problems 2011

49. A boxer, with a 5kg fist, punches a heavy bag with a velocity of 25m/s. If the punch contacts the heavy bag (heavy bag mass is 25kg) for 0.3s. Calculate the acceleration of the heavy bag. (This is a 2 part problem.) 50. A carnival game requires you to knock over stuffed clowns at the NJ shore. You are given the option of picking a ball that is very bouncy or a big lump of clay. Both options have the same amount of mass. Assume you can throw them with equal speed and accuracy and you only get one throw. Which option would you choose? Why? 51. A 40 kg skater traveling at 4 m/s overtakes a 60 kg skater traveling at 2 m/s in the same direction and collides with her. a. Sketch the before and after situations b. Construct an impulse-momentum bar chart c. If they remain in contact after the collision, what is their final velocity?

a. b. c. d.

52. There is another accident at the corner of Clarksville Road and Route 571. Will is driving a 1600 kg Jeep east at 20 m/s and runs the red light. He collides with Ralph’s 2000 kg Honda moving west at 15 m/s. The cars stick together and slide for 6 m before coming to a stop. Sketch the before and after situations In what direction and at what speed do they move together after the collision? How long does it take the vehicles to stop? What is the force exerted on the Honda by the Jeep when the cars are stuck together? 53. Andrew, who has a mass of 60.0 kg is riding at 25 m/s in her sports car when she must suddenly slam on the brakes to avoid hitting a dog crossing the road. She is wearing her seatbelt that brings her body to a stop in 0.400 s. a. What average force did the seatbelt exert on her? b. If she had not been wearing her seatbelt, and the windshield had stopped her head in 0.001 s, what average force would the windshield have exerted on her? c. How many times greater is the stopping force of the windshield than the seatbelt?

Work and Energy Make sure you know how to: a) Choose a system and the initial and final states of a physical process b) Use Newton’s second law to analyze a physical process c) Use kinematics to describe motion 54. Describe two processes where an external force is exerted on a system object and there is no work done on the system 55. A system can possess energy but not work, Why? 56. When we use energy conservation ideas, how do we incorporate the force that Earth exerts on an object?

Buggé: Final Exam Review Problems 2011

57. Why, when friction cannot be neglected, is it useful to include both surfaces in the system when analyzing processes using the energy approach? 58. Two football players are running towards each other at high speeds. They collide and stop. Where did their kinetic energy go? What happened to their momentum. 59. Why is it important to choose the system of interest before attempting to analyze a process? 60. Imagine a collision occurs. Before the event, you measured the masses of the two objects and the velocities of the objects both before and after the collision. Describe how you could use this data to determine which type of collision had occurred. 61. Jim (mass 80 kg) moves on rollerblades on a smooth linoleum floor a distance of 4.0 m in 5.0 s. Determine the power of this process. 62. James and Kenny decide to go hiking and both weigh 60 kg. The mountain they choose to climb is 1600 m high. It takes Matt 15 minutes to reach the top, and it takes Acey 25 minutes. If they both climb straight up, who does more work climbing the mountain? Why? How much power does each student generate? 63. If an object’s speed increases by a factor of 5, what factor would the kinetic energy increase by? 64. Felicia is driving a 2000kg Volkswagen beetle at 20 m/s and then takes her foot off the gas pedal. The car eventually stops due to an effective friction force in the axels, air, and other things exerted on the car. If the friction force has an average magnitude of 1000 N, how far will the car travel before stopping? Specify the system and the initial and final states. Include a bar chart in your explanation. 65. An elevator cable breaks 10 m above the ground. The falling elevator has a mass of 1200 kg. The elevator falls, compresses a spring at the bottom of the shaft, and stops. The force constant of the spring (k) is 3.0 x 105 N/m. (a) What is the velocity of the elevator the instant before it touches the spring? (b) How far is the spring compressed? Specify the system and the initial and final states. Include bar charts in your explanation. 66. 24. As a traffic cop investigating a car accident, you want to determine how fast a car was moving before its driver began to brake. While braking, the car left skid marks that are 70 m long. According to your reference book, the mass of the car is 1600 kg and the coefficient of static friction between the tires and road is 0.2. Was the car traveling faster than the 40 mph speed limit? Fill in the table below to determine the car’s initial speed 67. In Metropolis, the comic book hero Superman uses his incredible strength to save the lives of countless ordinary citizens. One day, the braking system on a passenger bus fails when the bus is 50 m away from a busy intersection. The bus is moving towards the intersection at 5 m/s. If Superman exerts a force of 300 N on the bus, which has a mass of 1000 kg, will he be able to stop the bus before it reaches the busy intersection?

Buggé: Final Exam Review Problems 2011

68. Pose a problem Describe a real-life situation in which an external force does the following: a. Positive work on a system b. Positive work on a system but with a value that is less than that in part (a) c. Negative work on a system d. Zero work, even though an object in the system moves. 69. A sled slides down a frictionless hill that is 17.6 m high. At the bottom of the hill, the sled hits a long patch of rough snow that slows down the sled by exerting an average force of 190 N on the sled. The mass of the sled and riders is 86 kg. a. How fast is the sled traveling after sliding for 10 m on the rough snow? b. How far must the sled travel on the rough snow before it is traveling at ½ of its maximum speed? c. How far will the sled slide on the rough snow before it comes to rest?

Electrostatics Make sure that you know how to: a) how to identify a system and construct an energy bar-chart for it b) how to identify a system and construct a force diagram for it c) how to convert a force diagram and an energy bar-chart into a mathematical statement 70. How do people know that a plastic rod rubbed with felt is negatively charged and the glass rod rubbed with silk is positively charged? 71. Summarize the particle model of charging by direct contact. 72. You have a charged electroscope on your desk. How can you decide whether it is positively or negatively charged? 73. You have two identical small metal foil bits hanging on threads. You charge one of them, and then touch them together. Then you place them at a distance d from each other and measure the force with which they repel each other. Qualitatively, how will the force change if you keep the distance the same but after charging touch one of the bits with your hand? What assumptions did you make in coming up with your answer? 74. How can we reduce the electric potential energy of a system of two electrically charged objects? 75. Are electrostatic interactions the same as magnetic interactions? What is similar? What is different? 76. Why is it important to choose a system of interest when analyzing a process using Newton’s second law or the work-energy principle? 77. Two identical conducting spheres are placed with their centers 0.5 m apart. One conducting sphere has an excess charge of -6 µC and the other has an excess charge of +20 µC. What can you say about the force exerted by the conducting

Buggé: Final Exam Review Problems 2011

sphere of -6 µC on the conducting sphere of +20 µC and the force exerted by the +20 µC conducting sphere on the -6 µC conducting sphere? 78. You rub a plastic tube with felt and thereby transfer 15 electrons from the felt to the tube. a. Draw sketches that show the net charge on the tube and felt before and after rubbing them together. b. Write a math statement that describes the charge transfer for the felt. c. Write a math statement that describes the charge transfer for the tube. d. Explain why the felt and the tube are attracted to each other after having been rubbed together even though they don’t interact at all before they are rubbed together. This explanation should be based on your answers to b and c above. Make sure you use the terms charged, neutral, transfer and net charge correctly. 79. Two charged particles, A and B, are near each other, but not touching. A

B

a. What will happen to the force exerted on each particle if the charge on A is doubled? b. What will happen to the force exerted on each particle if the charge on B is doubled? c. What will happen to the force exerted on each particle if the charge on each particle is doubled? d. What will happen to the force exerted on each particle if their separation distance is doubled? e. What will happen to the force exerted on each particle if the charge on A is doubled and their separation distance is cut in half? 80. A 0.50-kg cart with a metal sphere, electrically charged q = + 2.0 x 10–5 C, starts at rest with its metal sphere 1.0 m to the right of a fixed sphere with a positive charge Q = + 3.0 x 10–4 C. When released, the cart travels toward a fixed sphere on the right with charge –Q. The fixed charged objects are separated by 10 m. How fast is the cart moving when its charged metal sphere is 1.0 m from the negatively charged fixed sphere on the right? +Q

q

–Q

+

+

–

81. A metal sphere has a mass of 1.22 kg and carries a charge of -3.34 x 10-9 C. Determine the size of the charge required to levitate the sphere 1.00 cm above the charge.

Buggé: Final Exam Review Problems 2011

82. A small, lightweight hollow metal ball, initially uncharged, is suspended from a string and hung between the two spheres. It is observed that the ball swings rapidly back and forth, hitting one sphere and then the other. This goes on for 5 seconds, but then the ball stops swinging and hangs between the two spheres. Explain in detail, step by step, why the ball swings back and forth, and why it finally stops swinging. Include diagrams in your explanation

Electric Fields Make sure you know how to: a) find the force that one charged object exerts on another charged object b) determine the electric potential energy of a system c) explain the difference between the internal structure of electric conductors and dielectrics (non-conductors) 83. How do you calculate the electric field at a point located near two point-like charged objects? 84. What is the difference between the electric field produced by a point-like charged object and the electric field produced by large, uniformly charged plates? 85. Use the ideas of shielding to explain why you are safe in your car in a thunderstorm. 86. Three charged objects are shown. Determine the electric field at point A: at position x = 0.9 m.

87. An object with a charge of 2x10-8 C lies at rest. Calculate the electric field (a) 1m away and (b) 0.5m away. Why is this relationship with distance not linear?

DC Circuits Make sure you know how to: a) Apply the concept of electric field to understand electric interactions b) Explain the differences in internal structure between conducing materials and non-conducting materials 88. What condition(s) are needed for electric charge to travel from one place to another? 89. What is the physical quantity that is related to the cause of a continuous water flow through a hose and what is the physical quantity that is related to the cause of the continuous flow of electric charge through a bulb attached to a battery?

Buggé: Final Exam Review Problems 2011

90. What is the difference between series and parallel circuits? How can we tell how a circuit is wired? 91. What is Ohm’s law? Why is it useful? How did we learn about it? 92. Why does the resistance of a light bulb increase as the current through it increases? 93. Suppose two light bulbs of different resistance have the same potential difference across them. Is the rate of transformation of electric potential energy into thermal energy higher in the bulb with more resistance of less resistance? Explain 94. You have two resistors, R1 and R2 with R1 > R2. You first connect them in parallel to a battery; then connect them in series to a battery. Compare the total resistance of the parallel and series arrangements with the resistance of each individual resistor. 95. In what direction do electric charges move in a circuit and in what direction do they move inside a battery. 96. Know how to solve for current, potential difference, and resistance in both series and parallel circuits. 97. A 20 Ω, 30 Ω, and 40 Ω set of resistors are in parallel to a 12V battery. What is the potential difference across the 40 Ω resistor? (V) 98. A 20 Ω, 30 Ω, and 40 Ω set of resistors are connected in series to a 12 V battery. What is the current through the 40 Ω resistor? (A) 99. A complex circuit contains a 90 V battery followed by a 50 Ω resistor, followed by a parallel branch containing 40 Ω, 50 Ω, and 60 Ω resistors. The final resistor is 70 Ω. a) RT = ? b) Icircuit = ? c) Vparallel branch = ?

100. A 57V battery is connected to the following circuit. Find the following: a. Rtotal = ? b. Itotal = ? c. VR1 = ? d. IR2 = ? Given: R1 = 15Ω R2 = 40Ω R3 = 20Ω R4 = 20Ω R5 = 30Ω R6 = 30Ω V = 57V

R6

R5

R3

R4

R2 R1

57V

Buggé: Final Exam Review Problems 2011

101. Draw schematic diagrams for the following circuits: A battery attached to 3 resistors all in 2 resistors and a light bulb in series with parallel with an open switch on one two batteries branch

Optics Make sure you know how to: a) use a protractor to measure angles b) draw ray diagrams and normal lines c) use the laws of reflection and refraction 102. Why doesn’t the Sun cast semi shadows of objects? 103. How can we test the law of reflection? 104. Why is the expression ‘light travels in a straight line’ not accurate? 105. A mirror is hanging on a vertical wall. Will you see more of your body or less if you come closer to the mirror? 106. What is the difference between real and virtual images? 107. Compare and contrast concave mirrors and plane mirrors in terms of image formation. 108. How do we know how many rays an object sends onto a lens? 109. Where should you place an object with respect to a convex lens to have an image at exactly the same distance from the lens? What size is the image? 110. Locate the position, orientation, and type of image formed by an upright object held in front of a concave mirror of focal length +10 cm. The object distance is 54cm and is 10cm tall. Draw a ray diagram. 111. Locate the position, orientation, and type of image formed by an upright object held in front of a convex mirror of focal length (-5) cm. The object distance is 10cm and is 5cm tall. Draw a ray diagram. 112. Locate the position, orientation, and type of image formed by an upright object held in front of a concave mirror of focal length +50 cm. The object distance is 25cm and is 21 cm tall. Draw a ray diagram. 113. An object is 15.4 cm from a convex lens of +19.7cm focal length. The object is 15cm tall. Draw a ray diagram. 114. An object is 100 cm from a convex lens of +5cm focal length. The object is 25cm tall. Draw a ray diagram.

Buggé: Final Exam Review Problems 2011

115. An object is 5 cm from a concave lens of (-15cm) focal length. The object is 15cm tall