HONORS PHYSICS Linear Momentum

Transcription

1 HONORS PHYSICS Linear Momentum LESSON OBJECTIVES Students will be able to... understand that forces can act over time (impulse) resulting in changes in momentum identify characteristics of motion with respect to momentum in a collision distinguish between elastic and inelastic collisions state the Law of Conservation of Momentum SKILLS Students will be able to... use appropriate metric units for given measurements use steps for solving physics problems solve problems using mass, velocity, momentum and conservation of momentum for inelastic collisions conduct experiments relating to momentum collect and display experiment data develop models of inelastic collisions VOCABULARY Newton s Third Law momentum impulse law of conservation of momentum collision Impulse-Momentum theorem Inelastic collision HOMEWORK The Impulse-Momentum Change Theorem #1: Momentum, reading and written homework pages 1-2 #2: Momentum and Impulse Connection, reading and written homework pages 3-4 #3: Real-World Applications, reading The Law of Momentum Conservation #4: The Law of Action-Reaction (Revisited), reading and written homework pages 5-8 #5: Momentum Conservation Principle, reading #6: Isolated Systems, reading #8: Using Equations as a "Recipe", reading and written homework pages 9-12 #9: Using Equations as a Guide, reading and written homework pages #10: Momentum Conservation in Explosions, reading

2 CONTENT OUTLINE I. The Impulse-Momentum Change Theorem A. Momentum a. Defined b. Calculating B. Impulse a. Defined b. Calculating C. Relation between impulse and momentum II. The Law of Conservation of Momentum A. Connection to Newton s Third Law B. C. Momentum Conservation Principle D. Isolated Systems a. Collision and Impulse Problems b. Perfectly inelastic collisions in one dimension

3 Momentum of a Single Object 1. What is the momentum of a 3000 kg truck traveling at 25 m/s? 2. A 1500 kg ferryboat has a momentum of kg m/s. What is the speed of the ferryboat? 3. A car travels at a constant speed of 24 m/s and has a momentum of kg m/s. What is the mass of the car? 4. An 8 kg bowling ball rolls at a constant speed of 3 m/s. What is the momentum of the ball? 5. A bicyclist travels at a constant speed of 7 m/s. What is the total mass of the bicycle and the boy, when the total momentum is 490 kg m/s? 6. When a 45 kg cannon ball leaves a barrel it has a momentum of kg m/s. What is the speed of the ball at the end of the barrel? 7. A 45 kg woman runs at a speed of 5.6 m/s. What is her momentum? 8. A certain bowling ball rolls at a constant speed of 5 m/s. If the momentum of the ball is 42.5 kg m/s, what is its mass? 9. What is the speed of a 0.25 kg arrow with a momentum of 8 kgm/s? 10. A 1500 kg car travels 400 m in 12 s. What is its momentum? 11. An electron has a mass of 9.1x10-31 kg. What is its momentum if it is travelling at a speed of 3.5x10 6 m/s? 12. A 3 kg stone is dropped from a height of 4 m. What is its momentum as it strikes the ground? 13. If a ball is rolling at a velocity of 1.5 m/sec and has a momentum of 10.0 kg m/sec, what is the mass of the ball? 14. What is the velocity of an object that has a mass of 2.5 kilogram and a momentum of 1,000 kg m/sec? 15. Tiger Woods hits 45.0-gram golf ball, giving it a speed of 75.0 m/sec. What momentum has Tiger given to the golf ball? Momentum of a System of Objects 16. Determine the momentum of a system that consists of two objects. One object, m1, has a mass of 6 kg and a velocity of 13 m/s towards the east and a second object, m2, has a mass of 14 kg and a velocity of 7 m/s in that same direction. 17. Determine the momentum of a system that consists of two objects. One object, m1, has a mass of 6 kg and a velocity of 13 m/s in the direction of the positive x-axis and a second object, m2, has a mass of 14 kg and a velocity 7 m/s in the direction of the negative x-axis.

4 18. Determine the momentum of a system that consists of three objects. One object, m1, has a mass of 7 kg and a velocity 23 m/s towards the north, a second object, m2, has a mass of 9 kg and a velocity 7 m/s towards the north and the third object, m3 has a mass of 5 kg and a velocity of 42 m/s towards the south. 19. Determine the momentum of a system of the two objects. One object, m1, has a mass of 35 kg and a velocity of 3.7 m/s towards the east and the second object, m2, has a mass of 57 kg and a velocity of 4.3 m/s towards the west. 20. Determine the momentum of a system of the two objects. One object, m1, has a mass of 35 kg and a velocity of 3.7 m/s towards the north and the second object, m2, has a mass of 57 kg and a velocity of 4.3 m/s towards the south. 21. Determine the momentum of a system that consists of three objects. One object, m1, has a mass of 12 kg and a velocity 120 m/s towards the east, a second object, m2, has a mass of 25 kg and a velocity 18 m/s towards the west and the third object, m3 has a mass of 1 kg and a velocity of 350 m/s towards the east. Change of Momentum and Impulse 22. A 3-kilogram ball is accelerated from rest to a speed of 10 m/sec. a. What is the ball s change in momentum? b. What is the impulse? c. If a constant force of 40 newtons is applied to change the momentum in this situation, for how long does the force act? 23. A 2,000-kilogram car uses a braking force of 12,000 newtons to stop in 5 seconds. a. What impulse acts on the car? b. What is the change in momentum of the car? c. What is the initial speed of the car? 24. A 60-kilogram high jumper lands on a mat after her jump. The mat brings her to a stop after 1 second. She was traveling at 5.0 m/sec when she landed on the mat. Note: The speed of the jumper at the top of her jump, before she started to fall toward the mat, was 0 m/sec. a. What is the change in momentum for the jumper? b. What is the force felt by the jumper upon impact with the mat? 25. A 0.5-kilogram soccer ball is kicked with a force of 50 newtons for 0.2 seconds. The ball was at rest before the kick. What is the speed of the soccer ball after the kick? 26. A baseball player hits a kilogram fastball traveling at 44.0 m/sec into center field at a speed of 50.0 m/sec. If the impact lasts for second, with what force does he hit the baseball? 27. Tow Sawyer launches his 180-kilogram raft on the Mississippi River by pushing on it with a force of 75 newtons. How long must Tom push on the raft to accelerate it to a speed of 2.0 m/sec? 28. In terms of impulse, why is the ride much more comfortable when an airplane is flying at constant speed versus when it is taking off or landing? 29. In certain martial arts, people practice breaking a piece of wood with the side of their bare hand. Use your understanding of impulse to explain how this can be done without injury to the hand.

5 30. If identical bullets are shot from a pistol and a rifle, a bullet shot from the rifle will travel at a higher speed than a bullet from the pistol. Why? (Hints: Assume shooting force is the same in each case. The barrel of the rifle is longer than the barrel of the pistol. 31. Boxers attempt to move with an opponent s punch when it is thrown. In other words, a boxer moves in the same direction as their opponent's punch. This movement may prevent a knockout blow being delivered by their opponent. Explain how. 32. Show that the relationship between impulse and the change in momentum is another way of stating Newton's second law of motion. 33. Mats in a gym, airbags, and padding in sports uniforms are used to protect people from being injured. 34. Explain why these soft objects used instead of rigid objects using your understanding of impulse and change of momentum. 35. A 1200 kg car accelerates from 13 m/s to 17 m/s. Find the change in momentum of the car. 36. A small object with a momentum of 6 kg m/s to the west approaches head-on a large object at rest. The small object bounces straight back with a momentum of 5 kg m/s. What is the change in the momentum of the small object? What is the impulse exerted on the small ball? What is the impulse exerted on the large object? 37. A 0.03 kg golf ball is hit off the tee at a speed of 34 m/s. The golf club was in contact with the ball for s. What is the average force on ball by the golf club? 38. A toy rocket achieves a velocity of 55 m/s after 3 s, when fired straight up. If the average force exerted by the engine is 28 N, what is the toy s mass? 39. A kg air jet accelerates from rest to 45 m/s before it takes off. What is the change in momentum of the jet? 40. A kg piece of clay is thrown into a wall and has a speed of 9 m/s before it strikes the wall. Find the change in momentum of the clay and the impulse exerted on the clay if it does not bounce from the wall. 41. A small bouncy ball with a momentum of 8 kg m/s to the left approaches head-on a large door at rest. The ball bounces straight back with a momentum of 6 kg m/s. What is the change in the momentum of the ball? What is the impulse exerted on the ball? What is the impulse exerted on the door? 42. A 0.07 kg tennis ball leaves a racket with a speed of 56 m/s. If the ball is in contact with the racket for 0.04 s, what is the average force on the ball by the racket? 43. A kg baseball reaches a speed of 36 m/s when a bat strikes. If the average force of 500 N was applied on the ball by the bat, what is the impact time? 44. A 0.17 kg hockey puck slows down from 54 m/s to 35 m/s when it slides on horizontal ice surface. Find the change in momentum of the puck? 45. A 0.01 kg bullet is fired at 250 m/s into a wooden block that is fixed. The bullet emerges from the block with a speed of 120 m/s. What is the change in momentum of the bullet?

6 46. A 0.05 kg tennis ball moves at a speed of 10 m/s and is struck by a racket causing it to rebound in the opposite direction at a speed 16 m/s. What is the change in momentum of the ball? What is the impulse exerted on the ball? What is the impulse exerted on the racket? 47. A 0.25 kg beach ball rolling at a speed of 7 m/s collides with a heavy exercise ball at rest. The beach ball bounces straight back with a speed of 4 m/s. That is the change in momentum of the beach ball? What is the impulse exerted on the beach ball? What is the impulse exerted on the exercise ball? 48. A 0.16 kg hockey puck is moving on an icy horizontal surface with a speed of 5 m/s. A player strikes the puck by a hockey stick, after the impact the puck moves in opposite direction with a speed of 9 m/s. If the puck was in contact with the stick for s, what is the average force on the puck by the stick? 49. A constant force of 12 N acts for 5 s on a 5 kg object. What is the change in object s velocity? 50. A small object with a mass of 1 kg moves in a circular path with a constant speed of 5 m/s. What is the change in momentum during ½ of period; one period? Good time to review 1. What is formula for momentum? What is the unit of momentum? 2. What is the difference between momentum and mass? 3. Which has greater mass, a bowling ball at rest or a rolling basketball? Which has greater momentum? 4. How can a rocket change direction when it is far out of space and is essentially in a vacuum 5. A boy stands in the middle of a perfectly smooth, frictionless, frozen lake. How can he set himself in motion? 6. When rain falls from the sky, what happens to its momentum as it hits the ground? 7. What is impulse? What is the unit of impulse? 8. What is the difference between impulse and momentum? How does impulse relate to momentum? 9. When a glass falls, will the impulse be greater if it lands on a plush carpet than if it lands on a hard floor? 10. When a small car meshes with a large truck in a head-on collision, which of these two experiences greater change in momentum? Conservation of Momentum 51. A 400-kilogram cannon fires a 10-kilogram cannonball at 20 m/sec. If the cannon is on wheels, at what velocity does it move backward? (This backward motion is called recoil velocity.) 52. "Big" Al stands on a skateboard at rest and throws a 0.5-kilogram rock at a velocity of 10.0 m/sec. "Big" Al moves back at 0.05 m/sec. What is the combined mass of "Big" Al and the skateboard?

7 53. As the boat in which he is riding approaches a dock at 3.0 m/sec, Jasper stands up in the boat and jumps toward the dock. Jasper applies an average force of 800 newtons on the boat for 0.30 seconds as he jumps. a. How much momentum does Jasper's 80-kilogram body have as it lands on the dock? b. What is Jasper's speed on the dock? 54. Daryl the delivery guy gets out of his pizza delivery truck forgetting to set the parking brake. The 2,000 kilogram truck rolls down hill reaching a speed of 30 m/sec just before hitting a large oak tree. The vehicle stops 0.72 seconds after first making contact with the tree. a. How much momentum does the truck have just before hitting the tree? b. What is the average force applied by the tree? 55. Two billion people jump up in the air at the same time with an average velocity of 7.0 m/sec. If the mass of an average person is 60 kilograms and the mass of Earth is kilograms: a. What is the total momentum of the two billion people? b. What is the effect of their action on Earth? 56. Tammy, a lifeguard, spots a swimmer struggling in the surf and jumps from her lifeguard chair to the sand beach. She makes contact with the sand at a speed of 6.00 m/sec leaving an indentation in the sand 0.10 meters deep. a. If Tammy's mass is 60. kilograms, what is momentum as she first touches the sand? b. What is the average force applied on Tammy by the sand beach? 57. When a gun is fired, the shooter describes the sensation of the gun kicking. Explain this in terms of momentum conservation. 58. What does it mean to say that momentum is conserved? 59. A 13,500 kg railroad freight car travels on a level track at a speed of 4.5 m/s. It collides and couples with a 25,000 kg second car, initially at rest and with brakes released. What is the speed of the two cars after collision? 60. A 40 kg girl skates at 3.5 m/s on ice toward her 65 kg friend who is standing still, with open arms. As they collide and hold each other, what is the speed of the couple? 61. A 50 kg boy jumps off the front of a 1.5 kg skateboard moving forward. Find the skateboard s velocity immediately after the boy jumps, assuming that the skateboard s initial velocity is 3.5 m/s and the boy s velocity when jumping off the front is 5 m/s. 62. A 0.01 kg bullet has a speed of 700 m/s before it strikes a 0.95 kg wooden block that is stationary on a horizontal frictionless surface and remains inside of it. What is the speed of the block after the bullet becomes embedded in it? 63. A cannon ball with a mass of 100 kg flies in horizontal direction with a speed of 600 m/s and strikes a railroad freight car filled with sand and initially at rest. The total mass of the car and sand is 25,600 kg. Find the speed of the car after the ball becomes embedded it the sand. 64. A 0.01 kg bullet is fired at a 0.5 kg block initially at rest. The bullet, moving with an initial speed of 400 m/s, emerges from the block with a speed of 300 m/s. What is the speed of the block after the collision? 65. A 50 kg boy jumps off the back of a 1.5 kg skateboard moving forward. Find the skateboard s velocity immediately after the boy jumps, assuming that the skateboard s initial velocity is 3.5 m/s and the boy s velocity when jumping off the back is 5 m/s.

8 66. Two football players with mass 85 kg and 110 kg run directly toward each other with speeds 4 m/s and 7 m/s respectively. If they grab each other as they collide, what is the combined speed of the players just after the collision? 67. An air track car with a mass of 0.55 kg and velocity of 5.8 m/s to the right collides and couples with a 0.45 kg car moving to the left with a velocity of 3.9 m/s. What is the combined velocity of the cars just after the collision? 68. An air track car with a mass of 0.25 kg and velocity of 3.4 m/s to the right collides and couples with a 0.45 kg car moving to the left with a velocity of 3.9 m/s. What is the combined velocity of the cars just after the collision? 69. A kg railroad car travels on a horizontal track with a constant speed of 12 m/s. A 6000 kg load is dropped onto the car. What will be the car s speed? 70. A 55 kg skater at rest on a frictionless rink throws a 3 kg ball, giving the ball a velocity of 8 m/s. What is the velocity of the skater immediately after? 71. A kg bullet is fired at a 1.5 kg block initially at rest. The bullet, moving with an initial speed of 500 m/s, emerges from the block with a speed of 400 m/s. What is the speed of the block after the collision? 72. A 40 kg surfer jumps off the front of a 20 kg surfboard moving forward. Find the surfboard s velocity immediately after the girl jumps, assuming that the surfboard s initial velocity is 8 m/s and the girl s velocity when jumping off the front is 3 m/s. 73. A 40 kg surfer jumps off the back of a 20 kg surfboard moving forward. Find the surfboard s velocity immediately after the girl jumps, assuming that the surfboard s initial velocity is 8 m/s and the girl s velocity when jumping off the back is 3 m/s. Harder problems 74. The diagram above shows a ballistic pendulum. A 10 g bullet is fired into the suspended 2 kg block of wood and remains embedded inside it. After the impact of the bullet, the block swings up to a maximum height h. If the initial speed of the bullet was 35 m/s: a. What was the momentum of the bullet before the collision? b. What was the velocity of the bullet-block system just after the collision? c. What is the maximum possible height of the bullet-block system?

9 A B 75. Two objects, A and B, with masses of 3.2 kg and 1.8 kg, move on a frictionless horizontal surface. Object A moves to the right at a constant speed of 5.1 m/s while object B moves to the right at a constant speed 1.4 m/s. They collide and stick together (a perfectly inelastic collision). a. Determine the total momentum of the system (both objects) before the collision b. Find the speed of the two objects after the collision 76. A small cube, with a mass of 25 g, slides along a frictionless horizontal surface at a constant speed of 18 m/s until it collides with, and sticks to, a large wooden 3.5 kg block. The large block is attached to the left end of a spring with a spring constant of 100 N/m as shown above. a. What is the momentum of the cube before the collision? b. Find the speed of the combined cube and block system just after the collision. c. How far will the cube-block system move before it stops? 77. A bullet of mass 0.01 kg is moving horizontally with a speed of 100 m/s when it hits a block of mass 2 kg that is at rest on a horizontal surface with a coefficient of friction of 0.4. After the collision the bullet becomes embedded in the block. a. What is the net momentum of the bullet-block system before the collision? b. What is the net momentum of the bullet-block system after the collision? c. What is the speed of the bullet-block system after the collision? d. Find the maximum traveled distance of the bullet-block after the collision?

10 78. A 35 kg child moving at 5 m/s jumps onto a 40 kg sled that is initially at rest on a horizontal ice surface with the coefficient of friction of a. Determine the total momentum of the child-sled system before the child jumps onto the sled. b. Determine the total momentum of the child-sled system after the child jumps onto the sled. c. Determine the velocity of the child-sled system after the child jumps onto the sled. d. Determine the maximum horizontal distance that child-sled can go after the child jumps onto the sled? Practice Multiple Choice Questions 1. A freight car of mass 20,000 kg moves along a frictionless level railroad track with a constant speed of 15 m/s. What is the momentum of the car? A. 30,000 kg m/s D. 3,000,000 kg m/s B. 3,000 kg m/s E. 300 kg m/s C.300,000 kg m/s 2. A 500 kg sailboat moves with a momentum of 150,000 kg m/s? What is the velocity of the boat? A. 300 m/s B. 3 m/s C. 30 m/s D. 3,000 m/s E. 30,000 m/s 3. The momenta of two different objects are presented by on the diagram. Which of the following is the net momentum of the system of two objects? A. B. C. D. E.

11 4. The momenta of two different objects are presented by on the diagram. Which of the following is the net momentum of the system of two objects? A. B. C. D. E. 5. A cannon fires a cannonball and recoils backward. Which of the following statements is true about the cannon recoil? A. It happens because the energy of the system is conserved B. It happens because the energy of the system is increased C. It happens because the momentum of the system is not conserved D. It happens because the momentum of the system is conserved E. It happens because the momentum of the system is increased 6. An air balloon hovers at a certain altitude above the ground. A pilot throws a sand bag down from the balloon. What is the direction of the balloon s velocity just after the bag was thrown? A. B. C. D. E.

12 7. What is the momentum of the cannon after firing a cannon ball with an initial momentum of 5,000 kg m/s to the right? A. 5,000 kg m/s to the right B. 5,000 kg m/s to the left C. zero D. 2,500 kg m/s to the right E. 2,500 kg m/s to the left 8. A platform moves at a constant velocity on a horizontal surface. What happens to the velocity of the platform after a sudden rain falls down? A. It increases because the energy is conserved B. It decreases because the energy is conserved C. It remains constant because the momentum is conserved D. It increases because the momentum is conserved E. It decreases because the momentum is conserved 9. A stationary skateboarder I with a mass of 50 kg pushes a stationary skateboarder II with a mass of 75 kg. After the push the skateboarder II moves with a velocity of 2 m/s to the right. What is the velocity of the skateboarder I? A. 3 m/s to the left B. 2 m/s to the left C. 1 m/s to the right D. 3 m/s to the right E. 2 m/s to the right 10. A loaded freight car A with a mass of 24,000 kg moves at a constant velocity of 8 m/s on a horizontal railroad track and collides with an empty stationary car B with a mass of 8,000 kg. After the collision the cars stick to each other and moves like one object. What is the velocity of two cars after the collision? A. 2 m/s B. 4 m/s C. 6 m/s D. 8 m/s D. 12 m/s

13 11. A 40 kg skateboarder runs at a constant velocity of 0.12 m/s and jumps of a stationary skateboard with a mass of 8 kg. What is the velocity of the skateboard after the jump? A m/s B m/s C m/s D m/s E m/s 12. An 80 kg diver jumps off a moving boat. The boat has a mass of 400 kg and moves at a constant velocity of 2 m/s. What is the velocity of the boat after the jump if the diver jumps with a velocity of 3 m/s in opposite direction to the initial velocity of the boat? A. 2 m/s B. 3 m/s C. 4 m/s D. 5 m/s E. 6 m/s 13. Block A with a mass 2m moves on a frictionless horizontal surface at a constant speed v and collides and sticks with B of mass m. What is the velocity of two blocks after the collision? A. v B. v C. v D. v E. v 14. A 10 kg object moves at a constant velocity 2 m/s to the right and collides with a 4 kg object moving at a velocity 5 m/s to the left. Which of the following statements is correct? A. The total momentum before and after the collision is 20 kg m/s B. The total momentum before and after the collision is 40 kg m/s C. The total momentum before and after the collision is 10 kg m/s D. The total momentum before and after the collision is 30 kg m/s E. The total momentum before and after the collision is zero 15. A big truck collides with a small car. Which of the following statements is true? A. The truck experiences the greater magnitude of impulse during the collision B. The car experiences the greater magnitude of impulse during the collision C. They experience the same magnitude of impulse during the collision D. The impulse of each object is zero during the collision E. More information is required

14 16. A tennis ball approaches a racket with a momentum of 5 kg m/s and bounces back with a momentum of 6 kg m/s after the collision with the racket. What is the change in momentum of the tennis ball? A. 1 kg m/s B. 5 kg m/s C. 6 kg m/s D. 11 kg m/s E. 0 kg m/s 17. A rubber ball moving with an initial momentum Pi collides elastically with a vertical wall. Which of the following is correct about the vector of impulse that the ball experiences during the collision? A. B. C. D. E. 18. A piece of clay moving with an initial momentum Pi collides with a vertical wall and sticks to it. Which of the following is correct about the vector of impulse that the clay experiences during the collision? A. B. C. D. E.

15 19. The force as a function of time is presented by the graph. What is the impulse exerted on the object during first six seconds? A. 40 N s B. 80 N s C. 120 N s D. 240 N s E. 360 N s