PHYSICS 50 Lecture 7 1 RICHARD CRAIG Homework

PHYSICS 50: Lecture 7 -1 RICHARD CRAIG

Homework #6 n n n Read Chapter 7 Exercises and Problems: 7. 5, 7. 14, 7. 29, 7. 38, 7. 46, 7. 55 Due Thursday, 3/13

Potential Energy n n 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 n Ug = mgh

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

Q 7. 4 Concept Question The two ramps shown are both frictionless. The heights y 1 and y 2 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.

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.

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

Conservative forces

Q 7. 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 y 2. v 2 = 0 y 2 What is the speed of the ball when it is at a height of y 2/2? Ignore air resistance. v 1 = 20. 0 m/s m = 0. 150 kg 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 y 1 = 0

Conservation of Mechanical Energy

Around the Loop

Diver on a spring Board