Physics 121, Sections 9, 10, 11, and 12 Lecture 14 Today's Topics Homework 6 Chap6:#6,12,20,24,29,38,52,57,78,and83 Midterm 1: solutions Chapter 6: Work and Energy Review: Kinetic and Potential energy Non-conservative forces Generalized work-kinetic energy theorem Power Physics 121: Lecture 14, Pg 1
Physics 121: Lecture 14, Pg 1 Physics 121, Sections 9, 10, 11, and 12 Lecture 14 Today’s Topics: Homework 6: Chap. 6: # 6, 12, 20, 24, 29, 38, 52, 57, 78, and 83. Midterm 1: solutions Chapter 6: Work and Energy Review: Kinetic and Potential energy Non-conservative forces Generalized work-kinetic energy theorem Power
Definition of work Ingredients: Force(F), displacement (Ar) Work W. of a constant force F acting through a displacement A r is F W=F△rcos0 0/△r Physics 121: Lecture 14, Pg 2
Physics 121: Lecture 14, Pg 2 Definition of Work: Ingredients: Force ( F ), displacement ( r ) Work, W, of a constant force F acting through a displacement r is: W = F r cos F r Fr
Work Kinetic-Energy Theorem INet Work done on object] Change in kinetic energy of object W=△K K-K mv mV Physics 121: Lecture 14, Pg 3
Physics 121: Lecture 14, Pg 3 Work Kinetic-Energy Theorem: {Net Work done on object} = {change in kinetic energy of object} Wnet = K = K2 − K1 2 1 2 2 mv 2 1 mv 2 1 = −
Potential Energy Recap For any conservative force we can define a potential energy function U such that AU=U-U=-W The potential energy function U is always defined only up to an additive constant You can choose the location where u=o to be anywhere convenient Physics 121: Lecture 14, Pg 4
Physics 121: Lecture 14, Pg 4 Potential Energy Recap: For any conservative force we can define a potential energy function U such that: The potential energy function U is always defined only up to an additive constant. You can choose the location where U = 0 to be anywhere convenient. U = U2 - U1 = - W
Conservative Forces Potential Energies (stuff you should know): Force Work Change in P.E P.E. function F W(1-2) △U=U2-U Fg=-mg j -mg(y2-yi) mg) mgy +C GMm GMm GMm GMm IR2 R 尺,R R Fs=-kX KIx Physics 121: Lecture 14, Pg 5
Physics 121: Lecture 14, Pg 5 Conservative Forces & Potential Energies (stuff you should know): Force F Work W(1-2) Change in P.E U = U2 - U1 P.E. function U Fg = -mg j Fg = r Fs = -kx ^ ^ − 2 R1 1 R 1 GMm − − 1 2 2 2 1 2 k x x -mg(y2 -y1 ) mg(y2 -y1 ) − − GMm R R 1 1 2 1 1 2 2 2 1 2 k x − x − GMm R 2 mgy + C C R GMm − + kx +C 2 2 1