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PHYS16 – Lecture 19

PHYS16 – Lecture 19. Ch. 9 Momentum and Collisions. Announcements. Meet in parking lot behind Merrill on Wednesday! We will do a demo then come back to class…. Energy Post-question.

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PHYS16 – Lecture 19

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  1. PHYS16 – Lecture 19 Ch. 9 Momentum and Collisions

  2. Announcements • Meet in parking lot behind Merrill on Wednesday! • We will do a demo then come back to class…

  3. Energy Post-question • Two balls have the same mass. Ball 1 is thrown upward at 3 m/s and Ball 2 is thrown downward with 3 m/s. Which Ball reaches the ground with more kinetic energy? • Ball 1 • Ball 2 • Both balls have the same kinetic energy • There is not enough information

  4. Energy Post-question • If a car engine for a 1400 kg car outputs 1000 kW of average power, how much time does it take to accelerate from 0 to 25 m/s? • 0.4 s • 1 s • 0.2 s • 0.8 s • 10 s

  5. Energy Post-question • The potential energy, U (x), is shown as a function of position, x, in the figure. In which region is the magnitude of the force the highest? A) B) C) D)

  6. Energy Post-question • Clyde, the dinosaur, is sick of his doll-sized roller coaster and decides to ride the 20-m tall roller coaster at Ohio’s Cedar Point. Since Clyde is a little scared he decides to start from a location on the track that is 10 m lower than the top. How does Clyde’s speed at the bottom compare to a rider that started from the top of the hill? A) It is slower by a factor of 4. B) It is slower by a factor of 2√2. C) It is slower by a factor of 2. D) It is slower by a factor of √10 E) None of the above

  7. Ch. 9 Momentum & Collisions • Linear Momentum • Related to Newton’s second law • Rocket Propulsion • Momentum Conservation • Collisions • Elastic vs. Inelastic • 1D and 2D • Impulse

  8. Momentum • Momentum = mass times velocity • ↑ mass , then ↑ momentum • ↑ velocity, then ↑ momentum • Vector quantity • Units are (kg∙m/s)

  9. Discussion Question • If two objects have the same inertia, do they have the same momentum? • Two cars of equal mass are traveling around a round-a-bout. If object 1 has twice the momentum of object 2, what is the ratio of the centripetal force acting on each? What about the ratio of their kinetic energies? • If we have inertia and kinetic energy, why do we need momentum?

  10. 1. Momentum and Newton’s Second Law • In Newton’s second law F≠ ma!

  11. Rockets… http://exploration.grc.nasa.gov/education/rocket/gallery/delta/DeltaII.jpg http://www.youtube.com/watch?v=CAAhQ6xcAnw

  12. 2. Momentum Conservation • According to Newton’s third law momentum is conserved in an isolated system

  13. Medicine Ball and Skateboard… University of Maryland Physics Demo Facility

  14. Elastic and Inelastic Collisions • Perfectly Elastic – no losses due to the interaction • Objects bounce perfectly off one another • Ex. pool balls, gliders on air track • Inelastic – there are losses • Objects don’t perfectly bounce • Ex. basketball hitting ground • Perfectly Inelastic – objects adhere • Ex. clay ball with floor

  15. Conservation Laws • Perfectly Elastic – both momentum and energy conserved • Inelastic – only momentum conserved • Perfectly Inelastic – only momentum conserved

  16. Conclusions • Momentum • Momentum Conservation • Elastic vs. Inelastic Collisions

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