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Warm-Up: November 28, 2011

Warm-Up: November 28, 2011. Consider a baseball bat hitting a baseball. How does the force of the bat on the ball compare to the force of the ball on the bat? How do the directions of motion of the ball and bat compare before the collision?

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Warm-Up: November 28, 2011

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  1. Warm-Up: November 28, 2011 • Consider a baseball bat hitting a baseball. • How does the force of the bat on the ball compare to the force of the ball on the bat? • How do the directions of motion of the ball and bat compare before the collision? • How do the directions of motion of the ball and bat compare after the collision? • Which object has the larger acceleration? Why? • Reminder: word search is due tomorrow

  2. Momentum Chapter 9

  3. Momentum • The momentum of an object is equal to its mass times its velocity • Is represented by a lower case “p” • Is a vector (has magnitude and direction) • Has units of kg· m/s • Equivalent to N· s

  4. Example 1 • Calculate the momentum of a 103 kg linebacker running towards the quarterback at a speed of 7.5 m/s

  5. You-Try #1 • Calculate the momentum of a 141 kg lineman “running” at a speed of 2.1 m/s

  6. Impulse • The impulse acting on an object is equal to the force acting on it multiplied by the time interval over which it acts • Is represented by a capital “J” • Has same units as momentum, kg· m/s = N· s

  7. Example 2 • A 25 N force acts on a wooden box for 1.2 seconds. Calculate the impulse.

  8. You-Try #2 • A man pushes a heavy sofa for 3.7 seconds with an average force of 275 N. Calculate the impulse.

  9. Impulse-Momentum Theorem • The impulse acting on an object is equal to the object’s change in momentum

  10. Example 3 • A baseball has a mass of 0.145 kg. A pitcher throws it with a velocity of -41.3 m/s. The bat hits the ball with a force of 130 N for 0.100 seconds. What is the ball’s velocity after it leaves the bat?

  11. You-Try #3 • A hockey puck has a mass of 0.115 kg. A player hits it towards the goal with a velocity of -28.7 m/s. The puck misses the goal, and instead hits the goalpost with a force of 73.6 N for 0.070 seconds. What is the puck’s rebound velocity?

  12. Warm-Up: November 29, 2011 • A 17 kg bucket of water is being pulled out of a well by a rope with a tension of 210 N. • Draw a free body diagram of the bucket. • What is the acceleration of the bucket? • Have your homework (Unit 3 word search) in front of you for Mr. Szwast to check. • Show Mr. Szwast a correct and complete warm-up to receive today’s worksheet

  13. Momentum Worksheet • For #10, be careful with directions and positives and negatives. • Anything you do not finish in class is homework due Friday.

  14. Warm-Up: November 30, 2011 • A rocket sled is gliding across frictionless ice. It is moving at 120 m/s before it turns on a 4.0 second rocket boost that provides an average thrust of 5500 N. After the boost, the rocket is traveling at 210 m/s. What is the mass of the rocket?

  15. When Balls Collide… • Ball A and Ball B are rolling towards each other and collide. What happens? • It depends on the mass and velocity of each ball. • It also depends on the conditions of the system

  16. System Definitions • System: The set of objects which are being analyzed. • Closed system: A system in which no mass enters or leaves the system. • Isolated system: A system with no net external forces (or small enough to be negligible).

  17. Conservation of Momentum • The momentum of any closed, isolated system does not change. • For two objects in one dimension:

  18. Example 4 • A black ball with mass 1.4 kg and velocity 1.7 m/s is rolling towards a stationary gold ball with mass 0.40 kg. After the collision, the gold ball’s velocity is 1.5 m/s. What is the final velocity of the black ball?

  19. You-Try #4 (Warm-Up: December 2, 2011) • A white ball with mass 1.0 kg and velocity 1.0 m/s is rolling towards a blue ball with mass 0.75 kg and velocity -1.5 m/s. After the collision, the white ball’s velocity is -0.15 m/s. What is the final velocity of the blue ball?

  20. Example 5 • A bullet with mass 0.025 kg and velocity 550 m/s is shot into a 20.0 kg stationary wooden block that is on frictionless ice. The bullet gets lodged in the block and they travel together. What is the speed of the block and bullet?

  21. You-Try #5 • Two cars are driving towards each other. One has a mass of 1200 kg and a velocity of 24 m/s. The other has a mass of 1350 kg and a velocity of -19 m/s. The collision causes the two cars to be stuck together. What is the velocity of the two cars after the crash?

  22. Calculator Quiz! • 20 minute time limit • No talking while any quizzes are out • When finished, turn in your quiz, and pick up the “Conservation of Momentum” worksheet.

  23. Warm-Up: December 5, 2011 • A 1.7 kg rock is thrown into a stationary ball of clay at a speed of 3.2 m/s. The rock gets stuck in the clay and they move together at a speed of 2.3 m/s. What is the mass of the clay?

  24. Momentum and Impulse Key

  25. Types of Collisions • Elastic collisions conserve kinetic energy (we’ll talk about this next week). • Inelastic collisions do not conserve kinetic energy. • Perfectly inelastic collisions are where the colliding objects stick together and have the same final velocity. • A bullet shot into a wooden block • Two balls of clay that stick together

  26. Assignments • Conservation of Momentum WS due tomorrow • Homework due Wednesday: • Page 235 #7-9 • Page 250 #32-34, 38, 40, 57, 73, 80

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