9 Momentum and Its Conservation 2 Conservation of Momentum MAINIDEA

Transcription

1 9 Momentum and Its Conservation 2 Conservation of Momentum MAINIDEA Write the Main Idea for this section. REVIEW VOCABULARY Recall and write the definition of the Review Vocabulary term. NEW VOCABULARY closed system isolated system law of conservation of law of conservation of angular Use your book to define each term. closed system isolated system law of conservation of law of conservation of angular 142

2 Student Edition, pp Summarize information about the collision of two balls. GET IT? Explain the difference between a closed system and an isolated system. See the next page for a problem about. Draw an example of recoil. On the lines below, explain your example. 143

3 Student Edition, p. 246 Use with Example Problem 3. Use this column for scratch work and sketches. Problem Railroad car A, with mass 6275 kg, is traveling east at 6.5 m/s along a straight track. It strikes Railroad car B, with mass 5155 kg, which is also traveling east along the same track at 3.8 m/s. The two railroad cars stick together. Assume the track is frictionless. How fast do the two attached railroad cars move immediately after the collision? 1. ANALYZE AND SKETCH THE PROBLEM KNOWNS UNKNOWNS m A = m B = =? v Ai = v Bi = 2. SOLVE FOR THE UNKNOWNS Define the system: Write p i = p f in terms of the cars' masses and velocities. Rewrite this equation in terms of the velocity, v f, after the collision. Solve the equation for v f. 3. EVALUATE THE ANSWER Is the magnitude realistic? 144

4 Student Edition, pp Summarize the process in which a rocket in space changes velocity using rocket fuel. Describe features of two-dimensional collisions by filling in the missing terms. The law of conservation of holds for all systems with no forces. In order for a system to be isolated, you have to ignore. When a moving object strikes a stationary object, the moving object's initial equals the of the final s of the objects. The sum of the components of the before and after the collision must also be equal. See the next page for a problem about a two-dimensional collision. Compare and contrast linear and angular by completing the diagram. Linear mv force Is equal to... Is conserved is the system experiences no... Law of Conservation Angular p i = p f 145

5 Student Edition, p. 250 Use with Example Problem 5. Use this column for scratch work and sketches. Problem A 1445-kg car, C, moving east at 21.2 m/s, collides with a 2625-kg car, D, moving south at 17.5 m/s, and the cars stick together. In what direction and with what speed do they move after the collision? 1. ANALYZE AND SKETCH THE PROBLEM KNOWNS UNKNOWNS m c = v Ci,x = =? m D = v Di,y = =? 2. SOLVE FOR THE UNKNOWNS Determine the magnitudes of the initial momenta of the cars. Set up equations for p f,x and p f,y. Determine the final, p f. Solve for θ. Determine the final speed. 146

6 Student Edition, pp (continued) 3. EVALUATE THE ANSWER Does the angle's sign make sense? GET IT? Analyze Why does Earth precess as it rotates? SUMMARIZE How does the MAINIDEA for this section relate to the chapter s BIGIDEA? REVIEW IT! 30. MAINIDEA The outer rim of a plastic disk is thick and heavy. Besides making it easier to catch, how does this affect the rotational properties of the plastic disk? 31. Speed A cart, weighing 24.5 N, is released from rest on a 1.00-m ramp, inclined at an angle of 30.0 as shown in Figure 16. The cart rolls down the incline and strikes a second cart weighing 36.8 N N 1.00 m N a. Define the two carts as the system. Calculate the speed of the first cart at the bottom of the incline. b. If the two carts stick together, with what initial speed will they move along? Figure

7 32. Conservation of Momentum During a tennis serve, the racket of a tennis player continues forward after it hits the ball. Is conserved in the collision between the tennis racket and the ball? Explain, making sure you define the system. 33. Momentum A pole-vaulter runs toward the launch point with horizontal. Where does the vertical come from as the athlete vaults over the crossbar? 34. Initial Momentum During a soccer game, two players come from opposite directions and collide when trying to head the ball. The players come to rest in midair and fall to the ground. Describe their initial s. 34. Critical Thinking You catch a heavy ball while you are standing on a skateboard, and then you roll backward. If you were standing on the ground, however, you would be able to avoid moving while catching the ball. a. Identify the system you use in each case. b. Explain both situations using the law of conservation of. 148