p140w07_ct_11

# p140w07_ct_11 - Racquetball Striking a Wall Copyright:...

This preview shows pages 1–7. Sign up to view the full content.

Physics 140: Winter 2007 Lecture #11 February 8, 2007 Dave Winn Racquetball Striking a Wall Copyright: Loren M. Winters Mt. Etna Andrew Davidhazy

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Quick review • Objects in motion have kinetic energy: KE = ½ mv 2 • Kinetic energy is changed when forces act along the direction of motion • Work quantifies this: • The work-energy theorem describes changes in kinetic energy • To calculate the work done by a force (or forces) just add up the work in each little part of the path ds F s d F W along = = r r W Σ = Δ KE = s d F W r r
A cart on an air track is moving at 0.5 m/s when the air is suddenly turned off. The cart comes to rest after traveling 1 m. The experiment is repeated, but now the cart is moving at 1 m/s when the air is turned off. How far does the cart travel before coming to rest? 1: 1 m 2: 2 m 3: 3 m 4: 4 m 5: 5 m W = -F f d stop = Δ KE The work done by friction removes all the KE. When we double the starting speed the required Δ KE is 4x as large. Since the F f is the same, d stop must increase by 4x…

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Work and travel in curved paths • When the direction of motion or of forces changes, total work is summed over all little elements of the path • Calculate the dot product for each piece and sum = s d F W r r mg ds θ ( ) () mgdh s d F dh ds mgds s d F = = = r r r r θ cos cos
Work done by gravity • For gravity, the work done on any little segment is -mgdh • The total work will be: () i f y y mg dh mg mgdh s d F W = = = = r r mg ds θ mgdh s d F = r r A B This is true for any path from A to B! The total work done by gravity as an object moves is only dependent on the height of the object at the beginning and end of the motion: W grav = -mg(y f -y i ) Gravity is conservative!

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
What does this mean?
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 04/04/2008 for the course PHYSICS 140 taught by Professor Evrard during the Fall '07 term at University of Michigan.

### Page1 / 25

p140w07_ct_11 - Racquetball Striking a Wall Copyright:...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online