Physics Semester 2 Final Exam Review Answers

Honors Physics Semester 2 Final Exam Review Answers 1600 kg 800 kg 9 m/s A truck with mass 1600 kg collides with a car with mass 800 kg at rest. They stick together and continue to move to the right. 1. What is the total momentum of the system before the collision? 9600 kgm/s 2. What happens to the total momentum of the system after the collision? total momentum before = total momentum after that’s the law! 3. What is the velocity of the pair after the collision 4 m/s 4. Compare the force of the truck on the car to the car on the truck during the collision. F truck on car = F car on truck N3LFP A 1.0 kg low-friction non-plunger cart is moving toward a 0.50 kg low-friction plunger. The carts collide and the spring is compressed and the carts momentarily come to a stop as shown. 5. How do the forces on each of the carts compare? The carts exert equal forces on each other N3LFP 6. How do the accelerations of each of the carts compare? The acceleration of the smaller mass cart is greater 7. How do the changes in momentum ∆p of the carts compare? The changes in momentum of each of the carts are equal and opposite 8. Why is it safer for a pole-vaulter fall onto a puffy mat than onto the ground? The puffy increases the stopping time thereby decreasing the stopping force 9. Is it possible for a bullet and a baseball to have the same momentum? Yes if the baseball is going slow and the bullet is going fast or they are both not moving  10. Why do you think medieval catapults had very long flinging arms? Longer arms means that the force applied lasts for more time giving the projectiles a lager change in velocity A Human Cannon Ball is a carnival trick where a person is launched from a giant cannon. Suppose that the person has a mass of 80 kg and the cannon a mass of 800 kg. When the daredevil is launched… 11. Which exerts more force, the cannon on the man or the man on the cannon? They exert equal forces on each other N3LFP 12. Based on mass which will have larger change in velocity the cannon or cannon ball? The man will move forward faster than the cannon moves backward because he has less mass 13. If the cannon applies an average force of 1000 N to the man for 0.50 seconds, at what speed does the man leave the cannon? 6.25 m/s 14. At what speed does the cannon move backward? 0.625 m/s Honors Physics Semester 2 Final Exam Review Answers Page 2 Imagine that a steel ball is swung in a horizontal circle at a constant speed. E 15. In what direction does the velocity of the ball point? The velocity always points tangent to the circular path D B 16. In what direction does the acceleration of the ball point? The acceleration always points toward the center 17. Are the forces balanced or unbalanced? How do you know? The forces are unbalanced – you know this because the velocity is changing directions so the ball is acceleration and acceleration means unbalanced forces C A Top View 18. In what direction does the unbalanced force on the ball point?? The unbalanced force always points toward the center (same as the acceleration) 19. What is the nickname we give to the unbalanced force on the ball? What provides that unbalanced force? U6S0 Unbalanced force = centripetal force and is provided (in this case) by the string 20. What provides the outward force on the ball? It’s a trick! There are no outward forces 21. If you increased the force on the ball by a factor of three what would happen to the speed of the ball? The speed would increase by a factor of 9 22. Look back at the original picture above. At the position shown the string breaks. Which path will the ball take? D 23. Describe the path of the ball after the string breaks. The ball will go in the direction of D because an object in motion will stay motion in a straight line To conduct a physics experiment we took some physics students and bicycles onto the high school track. The rider and bicycle have a total mass of 99 kg. On the bicycle he rode the 100 m turn in 8 seconds. The radius of the turn was 33 meters. 24. What is the average speed of the rider? 12.5 m/s 25. What is the centripetal force necessary for the runner to make the turn? 469 N 26. What provides the centripetal force necessary for the runner to make the turn? The friction between the track and the tires 27. In what direction must the runner lean to make the turn? When in circular motion you always lean inward toward the center – the direction of the acceleration 28. At what angle must the runner lean to make the turn? 25° 29. What is the minimum coefficient of friction necessary for the runner to take the turn without slipping? 0.47 Honors Physics Semester 2 Final Exam Review Answers Page 3 30. As the Earth orbits the Sun, how many forces are on the Earth (ignore any forces by the moon)? Just one, the sun pulling the earth inward 31. Where does the net (unbalanced) force on the Earth point? Inward toward the sun – that is what causes it to go in a circle 32. If the Earth were twice as far from the Sun, the force of gravity on the Earth would be about… One quarter of what it was 33. Which force is bigger the Earth on the Sun or the Sun on the Earth? F Earth on Sun = F Sun on Earth At the right is a picture of a comet moving in an elliptical orbit around a star. Assume that the comet moves from A to B to C. 34. At which of the locations in the orbit at the right is the force on the comet the greatest? The least? How do you know? F is the greatest at C and the least at A. The closer it is the greater the force. B A 35. At which of the locations in the orbit at the right is the comet moving the fastest? The slowest? How do you know? The comet is the fastest at C and slowest at A. The closer it is the faster it is going. 36. Draw an arrow at each position that shows the force on the comet by the star? 37. Draw an arrow at each position that shows the velocity of the comet? 38. Define: U6S12 A Year – the time it takes for the Earth to go around the sun once. A Day – the time it takes for the Earth to spin around once. A Month – the time it takes for the moon to go around the Earth once. Mercury is the closest planet to the sun. It has a mass of 3.30 x 1023 kg and a radius of 2.44 x 106 meters. 39. What is the acceleration due to gravity on Mercury? 3.8 m/s/s 40. What would be the gravitational force between a 200 kg astronaut and Mercury if he were standing on the surface? 760 N C Honors Physics Semester 2 Final Exam Review Answers Page 4 Pictured below is a new roller coaster. A physics student riding and the coaster car have a combined mass of 200 kg. The car is at rest at point A and there is no braking at point D. Assume no friction between the coaster car and the track. A C 125 m 60 m B 15 m D 41. Rank the total energy from least to greatest. The total amount of energy stays the same the whole time 42. Rank the gravitational energy from least to greatest. DBCA 43. Rank the kinetic energy from least to greatest. ACBD 44. Rank the speed of the cart from least to greatest. ACBD 45. What happens to the energy as the cart rolls from A to B? Some of the gravitational energy is converted to kinetic energy 46. Determine the student’s gravitational energy at point A. 250000 J 47. Determine the student’s kinetic energy at point A. 0 J (it is stopped) 48. At point B, her height is only 15 m. Determine her gravitational energy and kinetic energies at point B. Gravitational Energy = 30000 J Kinetic Energy = 220000 J 49. At point D the coaster is on the ground and still moving. How fast is it going at Point D? 50 m/s On a real rollercoaster friction (both from the track and the air) are very present. 50. Draw pie charts for a real rollercoaster as it moves from points A to B to C to D? G  K + G +T  G + K +T  K + T Honors Physics Semester 2 Final Exam Review Answers Page 5 A crane lifts a steel girder of mass 1000 kg to a height of 45 meters. 51. Did the crane do work on the girder? How do you know? Yes – the crane lifts the girder giving it gravitational energy. Work is the transfer of energy and the motor transfers electrical energy to gravitational energy 1000 kg 52. How much work was done by the crane’s motor? 450000 J 45 m 53. If the motor pulls the girder up in 30 seconds what is the power output of the motor? 15000 Watts m = 0.5 kg μ=0 k = 200 N/m x = 0.20 m μ = 0.60 d=1m A 0.50 kg block that was being pushed against a spring is released from rest. The spring pushes the block which slides along a rough surface and then up a frictionless ramp and comes to a stop near the top of the ramp. 54. What happens to the total energy of the system as the block is pushed off of the spring; slides over the rough surface and then up the hill? The total energy of the system stays constant 55. What is the speed of the block just after it leaves the spring? 4 m/s 56. What is the speed of the block as it leaves the rough surface? 2 m/s 57. To what vertical height does the block go? 0.2 m 58. Write one sentence that describes the spring constant. For every additional 1 meter you compress the spring you would need to apply an additional 200 N 59. What is the force that you would have to apply to hold the block against the spring? 40 N Honors Physics Semester 2 Final Exam Review Answers Page 6 60. List 3 examples of longitudinal wave. Sound Waves Earth Quake P-Waves Forward and backward slinky waves Tsunami Waves 61. List 4 examples of transverse waves. Water Waves Earth Quake S-Waves “The Wave” All Electromagnetic Waves A physics student shakes a slinky left and right so that waves are created. In the trial #1 she creates 2 waves every one second. In trial #2 she creates 6 waves every one second. In trial #3 the student pushed a slinky forward and back so that she creates 4 waves every one second. 62. Which is/are longitudinal waves? 3 63. Determine the frequency of trial #2. 6 waves/sec Trial 1 64. Determine the wavelength of trial #2. 2 meters/wave Trial 2 65. Determine the speed of the wave in trial #2? 12 meters/sec 66. Which (1 or 2) has the larger wavelength? 1 Trial 3 6m 67. Which trial (1 or 2) has the larger amplitude? 2 In trial #3 above the slinky is pushed back and forth with a frequency of 4 waves/second. You then halved the frequency to 2 waves/second. 68. What would happen to the wavelength? The wavelength would double (inverse relationship) 69. What would happen to the speed of the wave? The speed stays the same because it is still the same spring 70. Bored and watching surfing on TV you notice the motion of the surfers waiting to catch a wave. How are they moving as they encounter the waves? The surfers go up and down! The waves are transverse so the vibration is perpendicular to the direction of motion Honors Physics Semester 2 Final Exam Review Answers Page 7 Two wave pulses on a slinky are moving toward each other as shown. 71. Draw a “during” picture for these wave pulses. 72. Draw an “after” for these wave pulses. 73. Watching a baseball game at Comerica Park from the outfield seats there is a noticeable delay between when you see the batter hit the ball and the crack of the bat. What’s up with that? Sound waves travel slow compared to light waves. So the light gets to you way before the sound gets to you. 74. With a stop watch you find the delay to be 0.5 seconds. How far away is the batter? The speed of sound is 340 m/s. 170 meters away A water bug is sitting on the surface of a pond when a frog jumps in and disturbs the water. The bug makes 5 bobs up and down in 20 seconds and reaches a maximum height of 0.20 meters above still water. With his handy-dandy meter stick, he measures the length between crests of the wave to be 2 meters. After a few seconds, the height of the waves is only 0.10 meters. 75. What is the period of the waves? 4 seconds/wave 76. What is the frequency of the waves? 0.25 waves/second 77. What is the speed of the waves in the water? 0.5 meters/second 78. What happens to the speed of the wave as the amplitude becomes smaller? Nothing – the water is the same so the speed of the wave is the same (mechanical wave) Honors Physics Semester 2 Final Exam Review Answers Above are the regions of the electromagnetic Spectrum. 79. At you move left to right what happens to the frequencies? What happens to the wavelengths? U9S4 The frequencies increase and the wavelength decreases 80. As you move left to right what happens to the speeds? What happens to the energies? U9S4 The speeds stay the same and the energies increase 81. Why is it that radio waves can travel through space but sound waves cannot? U9S3 radio waves are electromagnetic waves and need no medium through which to travel sound waves are mechanical waves and need a medium for their existence 82. Compared the pitches of sounds made by long boom whackers to the pitches of sounds made by short boom whackers. Long boom whackers make low pitched sounds with small frequencies Small book whackers make high pitched sounds with large frequencies Short instruments like violins produce higher pitched notes thank long instruments like cellos. 83. How do the frequencies of the higher notes compare to the lower notes. high notes have large frequencies low notes have small frequencies Banging a tuning fork harder produces a louder note. 84. How do the waves created by the louder note compare to a softer note? louder waves have bigger amplitudes Page 8 Honors Physics Semester 2 Final Exam Review Answers Page 9 -7 Two charged metal spheres A and B are separated by a distance of 0.02 meters. Sphere A has a charge of +6.0 x 10 C and sphere B has a charge of +4.0 x 10-7 C. In addition, sphere B has twice the surface area as sphere A. 85. How will the spheres move if released? The will move away from each other – likes repel! 86. Which supplies more force? The apply the same forces on each other N3LFP A 87. Calculate the force of A on B. 5.4 N B d = 0.02 m 88. What happens to the force of A on B when the distance between the charged objects is cut in half? The force increases by a factor of 4