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Chapter 9 Momentum. Impulse Momentum The impulse-momentum theorem Conservation of momentum Inelastic collisions. Topics:. Sample question:. - PowerPoint PPT Presentation
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Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
• Impulse
• Momentum
• The impulse-momentum theorem
• Conservation of momentum
• Inelastic collisions
Chapter 9Momentum
Topics:
Sample question:
Male rams butt heads at high speeds in a ritual to assert their dominance. How can the force of this collision be minimized so as to avoid damage to their brains?
Slide 9-1
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Reading Quiz
1. Impulse is
A. a force that is applied at a random time.
B. a force that is applied very suddenly.
C. the area under the force curve in a force-versus-time graph.
D. the interval of time that a force lasts.
Slide 9-2
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
1. Impulse is
C. the area under the force curve in a force-versus-time graph.
Slide 9-3
Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Reading Quiz
2. The total momentum of a system is conserved
A. always.
B. if no external forces act on the system.
C. if no internal forces act on the system.
D. never; momentum is only approximately conserved.
Slide 9-4
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
2. The total momentum of a system is conserved
B. if no external forces act on the system.
Slide 9-5
Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Reading Quiz
3. In an inelastic collision,
A. impulse is conserved.
B. momentum is conserved.
C. force is conserved.
D. energy is conserved.
E. elasticity is conserved.
Slide 9-6
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
3. In an inelastic collision,
B. momentum is conserved.
Slide 9-7
Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Impulse
The force of the foot on the ball is an impulsive force.
Slide 9-8
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Graphical Interpretation of Impulse
J = Impulse = area under the force curve Favgt
Slide 9-9
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Momentum
Momentum is the product of an object’s mass and its velocity:
Slide 9-10
p = mv
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
The Impulse-Momentum Theorem
Impulse causes a change in momentum:
Slide 9-11
J =pf - pi = ∆p
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Example
A 0.5 kg hockey puck slides to the right at 10 m/s. It is hit with a hockey stick that exerts the force shown. What is its approximate final speed?
Slide 9-12
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Checking Understanding
Two 1-kg stationary cue balls are struck by cue sticks. The cues exert the forces shown. Which ball has the greater final speed?
Slide 9-13
A. Ball 1B. Ball 2C. Both balls have the same final speed
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Two 1-kg stationary cue balls are struck by cue sticks. The cues exert the forces shown. Which ball has the greater final speed?
Slide 9-14
C. Both balls have the same final speed
Answer
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 9-15
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
A car traveling at 20 m/s crashes into a bridge abutment. Estimate the force on the driver if the driver is stopped by
A. a 20-m-long row of water-filled barrels
B. the crumple zone of her car (~1 m). Assume a constant acceleration.
Example
Slide 9-16
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A 500 kg rocket sled is coasting at 20 m/s. It then turns on its rocket engines for 5.0 s, with a thrust of 1000 N. What is its final speed?
Example
Slide 9-17
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In terms of the initial and final total momenta:
The Law of Conservation of Momentum
In terms of components:
Slide 9-18
Pf = Pi
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 9-19
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Example
A curling stone, with a mass of 20.0 kg, slides across the ice at 1.50 m/s. It collides head on with a stationary 0.160-kg hockey puck. After the collision, the puck’s speed is 2.50 m/s. What is the stone’s final velocity?
Slide 9-20
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Inelastic Collisions
For now, we’ll consider perfectly inelastic collisions:
A perfectly elastic collision results whenever the two objects move off at a common final velocity.
Slide 9-21
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Example
Jack stands at rest on a skateboard. The mass of Jack and the skateboard together is 75 kg. Ryan throws a 3.0 kg ball horizontally to the right at 4.0 m/s to Jack, who catches it. What is the final speed of Jack and the skateboard?
Slide 9-22
Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley.
Example
A 10 g bullet is fired into a 1.0 kg wood block, where it lodges. Subsequently, the block slides 4.0 m across a floor (µk = 0.20 for wood on wood). What was the bullet’s speed?
Slide 9-23