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PHYSICS 50: Lecture 7-1

Delve into gravitational potential energy and conservation laws in physics with exercises and problems in Chapter 7. Answer concept questions on energy conservation and kinetic properties. Understand projectile motion and the impact of air resistance.

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PHYSICS 50: Lecture 7-1

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  1. PHYSICS 50: Lecture 7-1 RICHARD CRAIG

  2. Homework #6 • Read Chapter 7 • Exercises and Problems: 7.5, 7.14, 7.29,7.38, 7.46, 7.55 • Due Thursday, 3/13

  3. Potential Energy • Instead of considering how the work form gravity changes the kinetic energy of a system I can consider gravity a form of energy • Gravitational Potential energy • Ug = mgh

  4. Conservation of Energy • When no “outside” forces or friction then mechanical energy is conserved • Kinetic + Gravitational + Elastic = Constant • Total energy is always conserved

  5. Q7.4 Concept Question The two ramps shown are both frictionless. The heights y1 and y2 are the same for each ramp. A block of mass m is released from rest at the left-hand end of each ramp. Which block arrives at the right-hand end with the greater speed? A. the block on the curved track B. the block on the straight track C. Both blocks arrive at the right-hand end with the same speed. D. The answer depends on the shape of the curved track.

  6. Work and energy along a curved path • Notice the same expression for gravitational potential energy is the same along either a curved or straight path.

  7. Shoot bullet at same speed • Consider the speed of a projectile as it traverses its parabola in the absence of air resistance.

  8. Conservative forces

  9. v2 = 0 y2 v1 = 20.0 m/s m = 0.150 kg y1 = 0 Q7.2 Concept Questions #2 You toss a 0.150-kg baseball straight upward so that it leaves your hand moving at 20.0 m/s. The ball reaches a maximum height y2. What is the speed of the ball when it is at a height of y2/2? Ignore air resistance. A. 10.0 m/s B. less than 10.0 m/s but more than zero C. more than 10.0 m/s D. not enough information given to decide

  10. Conservation of Mechanical Energy

  11. Around the Loop

  12. Diver on a spring Board

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