PHYSICS 50: Lecture 7-1 RICHARD CRAIG

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

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 U g = mgh

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

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. Q7.4 Concept Question

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.

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

Conservative forces

You toss a kg baseball straight upward so that it leaves your hand moving at 20.0 m/s. The ball reaches a maximum height y 2. What is the speed of the ball when it is at a height of y 2 /2? Ignore air resistance. A 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 Q7.2 m = kg v 1 = 20.0 m/s v 2 = 0 y 1 = 0 y2y2 Concept Questions #2

Conservation of Mechanical Energy

Around the Loop

Diver on a spring Board