Physics S2 Final Exam Review Answers

Physics Semester 2 Final Exam Review Answers 1600 kg 800 kg 6 m/s A truck with mass16000 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? momentum before = momentum after that is 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 car on truck = F truck on car they are Newton’s 3rd Law Force Pairs 5. Why is it safer for the driver of the car to impact the airbag than the windshield? The air bag increases the stopping time thereby decreasing the stopping force 6. Is it possible for a bowling ball and a golf ball to have the same momentum? Yes – the bowling ball has to be slow and the golf ball fast to equal out the masses A Civil War cannon with mass 800 kg fires a cannon ball with mass 8 kg. 7. Which exerts more force, the cannon on the ball or the ball on the cannon? F cannon on ball = F ball on cannon they are Newton’s 3rd Law Force Pairs 8. Based on mass which will have larger change in velocity the cannon or cannon ball? U7S7 The ball has a bigger change in velocity because it has a smaller mass 9. If the cannon applies an average force of 10,000 N to the ball for 0.10 seconds, at what speed does the ball leave the cannon? 125 m/s Imagine that a steel ball is swung in a horizontal circle at a constant speed. E 10. In what direction does the velocity of the ball point? The velocity always points tangent to the circular path 13. In what direction does the unbalanced force on the ball point?? The unbalanced force always points toward the center (same as the acceleration) 14. What is the nickname we give to the unbalanced force on the ball? What provides that unbalanced force? unbalanced force = centripetal force and is provided (in this case) by the string C B 11. In what direction does the acceleration of the ball point? The acceleration always points toward the center 12. 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 D A Top View Physics Semester 2 Final Exam Review Answers Page 2 15. What provides the outward force on the ball? It’s a trick! There are no outward forces 16. If you wanted to increase the speed of the ball what would you have to do to the force on the string? Pull harder on the string; increase the inward force 17. Look back at the original picture above. At the position shown the string breaks. Which path will the ball take? D 18. 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 19. 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 20. Where does the net (unbalanced) force on the Earth point? Inward toward the sun – that is what causes it to go in a circle 21. 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 22. 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. 23. 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. 24. 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. 25. Draw an arrow at each position that shows the force on the comet by the star? 26. Draw an arrow at each position that shows the velocity of the comet? 27. Define: 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. B A C Physics Semester 2 Final Exam Review Answers Page 3 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 80 m 40 m B 5m 28. Rank the total energy from least to greatest. The total amount of energy stays the same the whole time 29. Rank the gravitational energy from least to greatest. DBCA 30. Rank the kinetic energy from least to greatest. ACBD 31. Rank the speed of the cart from least to greatest. ACBD 32. What happens to the energy as the cart rolls from A to B? The gravitational energy is converted to kinetic energy 33. Determine the student’s gravitational energy at point A. 160000 J 34. Determine the student’s kinetic energy at point A. 0 J (it is stopped) 35. At point B, her height is only 5 m. Determine her gravitational energy and kinetic energies at point B. Gravitational Energy = 10000 J Kinetic Energy = 150000 J 36. At point D the coaster is on the ground and still moving. How fast is it going at Point D? 40 m/s On a real rollercoaster friction (both from the track and the air) are very present. 37. 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 D Physics Semester 2 Final Exam Review Answers Page 4 A crane lifts a steel girder of mass 1000 kg to a height of 45 meters. 38. 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 39. How much work was done by the crane’s motor? 450000 J 40. If the motor pulls the girder up in 30 seconds what is the power output of the motor? 15000 Watts 45 m 41. List 3 examples of longitudinal wave. Sound Waves Earth Quake P-Waves Forward and backward slinky waves Tsunami Waves 42. 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 1 wave every one second. In trial #2 she creates 3 waves every one second. In trial #3 the student pushed a slinky forward and back so that she creates 2 waves every one second. 43. Which are transverse waves? 1 and 2 44. Determine the frequency of trial #2. 3 waves/sec Trial 1 45. Determine the wavelength of trial #2. 2 meters/wave Trial 2 46. Determine the speed of the wave in trial #2? 6 meters/sec Trial 3 6m 47. Which (1 or 2) has the larger wavelength? 1 48. Which trial (1 or 2) has the larger amplitude? 2 Physics Semester 2 Final Exam Review Answers Page 5 In trial #3 above the slinky is pushed back and forth with a frequency of 2 waves/second. You then doubled the frequency to 4 waves/second. 49. What would happen to the wavelength? The wavelength is cut in half 50. What would happen to the speed of the wave? Speed stays the same because it is still the same spring 51. Watching boats out on Lake St. Clair, some physics students see waves heading toward the boats. What happens to the boats as they encounter the waves? The boats go up and down! The waves are transverse so the vibration is perpendicular to the direction of motion Two wave pulses on a slinky are moving toward each other as shown. 52. Draw the “during” picture for these waves. 53. Draw the “after” picture for these waves. 54. 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. 55. 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 Physics Semester 2 Final Exam Review Answers Page 6 Above are the regions of the electromagnetic Spectrum. 56. At you move left to right what happens to the frequencies? What happens to the wavelengths? The frequencies increase and the wavelength decreases 57. As you move left to right what happens to the speeds? What happens to the energies? The speeds stay the same and the energies increase 58. Why is it that radio waves can travel through space but sound waves cannot? 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 59. 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. 60. 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. 61. How do the waves created by the louder note compare to a softer note? louder waves have bigger amplitudes Two charged metal spheres A are separated by a distance of 0.02 meters. 62. How will the spheres move if released? Why? They will move away from each other because like charges repel + + d = 0.02 m 63. Which supplies more force? U5S9 They supply the same forces on each other because of Newton’s 3 rd Law 64. What happens to the force when the distance between the charged objects is tripled? The force goes down by a factor of 9 because there is an inverse square relationship between force and distance