Momentum ~ Learning Guide Name:

Transcription

1 Momentum ~ Learning Guide Name: Instructions: Using a pencil, answer the following questions. The Pre-Reading is marked, based on effort, completeness, and neatness (not accuracy). The rest of the assignment is marked, based on effort, completeness, neatness, and accuracy. Every time you see a bold word, make sure you refer back to your "Submission Requirements." Do your best! Pre-Unit Thoughts: When you think of momentum, what do you think of? What are the factors that you think might change an object's momentum? Unit Notes & Practice: 1. Does a ball thrown upward lose momentum as it rises? Justify your answer. Page 1 of 10

2 2. If you (use your mass) were to jump off a small (200 kg), stationary boat in the lake horizontally at 5m/s, what happens to the boat? Show your calculations. 3. If you (use your mass) were to jump off a cruise ship (6.5 x 10 7 kg) horizontally at 5m/s, how much would the ship s velocity change? Show your calculations. 4. If a golf ball and a football have the same kinetic energy (Kinetic Energy = E k = ½ mv 2 and is measure in Joules as it represents the ENERGY of motion), which ball has the greatest momentum? Prove your answer algebraically. (Do an internet search for the mass of a golfball and a football. You may assume that the golfball comes off of the club at 40m/s) 5. Justify, in terms of momentum and impulse, the use of airbags in cars. Page 2 of 10

3 6. A rubber ball and a lump of putty, of equal mass, are thrown against a wall. The ball bounces while the putty sticks. Which imparts the biggest impulse? Justify your answer. 7. An atomic nucleus at rest decays radioactively into an alpha particle and a smaller nucleus. The alpha particle is observed to move off at a speed of 3.8 X 10 5 m/s. What will be the speed and direction (relative to the alpha particle) of the recoiling nucleus if the daughter nucleus is 57 times more massive than the alpha particle? Show your work. (Answer: 6700 m/s in opposite direction). 8. A 145 kg astronaut (including space-suit) acquires a speed of 2.50 m/s by pushing off with her legs from an 1850 kg space capsule. a) What is the change in speed of the space capsule? b) If the push lasts for sec, what is the average force exerted by each on the other? Consider a reference frame in which the space capsule is at rest before the pushing off. Show your work. (Answers: a) 0.20 m/s, b) 725 N) Page 3 of 10

4 9. Why is it difficult for a fire-fighter to hold a hose that ejects large amounts of high- speed water? Justify your answer first with Newton s Laws, then with the laws of momentum and/or Impulse. 10. If a Mack truck and a Volkswagen traveling at equal speeds have a head-on collision, which vehicle will experience the greatest force of impact? The greatest change in its momentum? The greatest acceleration? Justify with concepts learned. 11. Suppose there are three astronauts outside a spaceship, and two of them decide to play catch with the third man. All the astronauts weigh the same on earth and are equally strong. The first astronaut throws the second one toward the third one and the game begins. Describe the motion of the astronauts as the game proceeds. How long will the game last? Page 4 of 10

5 12. A billiard ball will stop short when it collides head-on with a ball at rest. The ball cannot stop short, however, it the collision is not exactly head on--that is, if the second ball moves at an angle to the path of the first. Momentum is ALWAYS conserved. Explain how momentum would be conserved in this two dimensional collision. You may use a diagram drawn to scale and labelled with the appropriate angles, or you may use a component argument. We are looking to see how one might solve such a question. 13. When you release the end of a full and untied balloon, what happens? Justify your answer with what you know about the physics of explosions? How does this relate to rockets? Page 5 of 10

6 14. A 5.0 g air pellet is fired into a 495 g sandbag, which is suspended by a string to form a pendulum. If the sandbag plus the imbedded pellet move off at 2.0 m/s immediately after the pellet hits the sandbag, what was the speed of the pellet just before it hit the sandbag? ). Show your work as shown in the lessons. (ans. 200 m/s) 15. A boy and his skateboard have a combined mass of 64 kg. If he is moving with a speed of 3.2 m/s, and collides with a stationary skateboarder whose mass (including his skateboard) is 96 kg, with what speed will the two skateboarders move immediately after the collision? Assume they are hopelessly entangled, but their wheels point in the same direction ). Show your work as shown in the lessons. (ans m/s) 16. The Titanic hit an iceberg estimated to be half of her mass. Before hitting the iceberg, the Titanic was estimated to be going 22 kts (11.3 m/s). After hitting the iceberg, the Titanic was estimated to be going about 6.0 knots (3.1 m/s). How fast was the iceberg going after the collision? Assume a head-on collision. Show your work as shown in the lessons. (ans m/s) Page 6 of 10

7 17. The eight situations Various similar boxes are being pushed for 10 seconds across a floor by a net horizontal force as shown below. The mass of the boxes and the net horizontal force for each case are given in the indicated figures. Rank the change in velocity for each box from the greatest change in velocity to the least change in velocity. All boxes have an initial velocity of 0 m/s (+ direction is to the right and - to the left with 4 < -2).. Greatest Least Carefully explain the reasoning behind your ranking. How sure were you of your ranking? (circle one) Basically Guessed Sure Very Sure Page 7 of 10

8 18. The eight situations below show before and after "snapshots" of a car's velocity. Rank these situations in terms of the Impulse acting on these cars, from most positive to most negative. All cars have the same mass. Negative numbers, if any, rank lower than positive ones (-20 m/s < -10 m/s < 0 < 5). Most Most Positive Negative Carefully explain the reasoning behind your ranking. How sure were you of your ranking? (circle one) Basically Guessed Sure Very Sure Page 8 of 10

9 19. A 5-kilogram ball initially rests at the edge of a 2-meter-long, 1.2-meter-high frictionless table, as shown above. A hard plastic cube of mass 0.5 kilogram slides across the table at a speed of 26 meters per second and strikes the ball, causing the ball to leave the table in the direction in which the cube was moving. The figure below shows a graph of the force exerted on the ball by the cube as a function of time. a. Determine the total impulse given to the ball. (ans. 12 Ns) Page 9 of 10

10 b. Determine the horizontal velocity of the ball immediately after the collision. (ans. v bf = 2.4 m/s) c. Determine the following for the cube immediately after the collision. i. Its speed (ans. v cf = 2 m/s) ii. Its direction of travel (right or left), if moving. (ans. since +, moving right) Page 10 of 10