Physics131_L18WI10

# Physics131_L18WI10 - Physics 131 Mechanics Le cture18 Fe...

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Physics 131 - Mechanics Lecture 18 February 24, 2010 Homeyra Sadaghiani

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On Friday, Feb 26th, we will have Exam 1, which covers Knight, Chapters 5-10 and my lectures 10-18. Exam 2 is closed-book, but you may bring with you one page of notes on a 8½x11” sheet of paper with your name on it and should turn it in with your exam. Bring a Scantron sheet and a calculator with good batteries. Exam 2 will have a multiple-choice section and a free-response section based on lecture example problems and end-of-chapter homework problems in Knight. Exam 2
Wee k Date L# Lecture topic Text reading HW 5 1-Feb 10 Equilibrium, using the 2nd Law 6.1-3 (12 P)   3-Feb 11 2nd Law Application: Friction, Drag 6.4-6 (12 P) HW# 4   5-Feb 12 Newton’s 3rd Law: Interaction 7.1-5 (19 P) 6 8-Feb 13 Uniform circular motion 8.1-7 (18 P)   10-Feb 14 Momentum, Impulse & conservation of momentum 9.1-3 (13 P) HW# 5   12-Feb F1 Conservation of momentum Tutorial 7 15-Feb H2 Holiday (Presidents' Day)   17-Feb 15 Inelastic collisions 9.4-6 (12 P) HW# 6   19-Feb 16 Energy 10.1-4 (13 P) 8 22-Feb 17 Potential energy and elastic collision 10.5-7 (13 P) 24-Feb 18 Work & kinetic energy 11.1-3 (10 P) HW# 7 26-Feb E2 EXAM 2- Chapters 5-10 Lecture Schedule We are here! 3

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Elastic Collisions October 24, 2010 Physics 131 - Lecture 17 4
Elastic Collisions Consider a head-on, perfectly elastic collision of a ball of mass m 1 having initial velocity ( v i x ) 1 , with a ball of mass m that is initially at rest . The balls’ velocities after October 24, 2010 Physics 131 - Lecture 17 5

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October 24, 2010 Physics 131 - Lecture 17 Elastic Collisions In elastic collisions, both kinetic energy and momentum are conserved. One-dimensional elastic collision: 6
October 24, 2010 Physics 131 - Lecture 17 Elastic Collisions in 1D 2 2 2 1 1 1 ( ) ( ) f i i f m v v m v v - = - 2 2 2 2 2 2 2 1 1 1 ( ) ( ) f i i f m v v m v v - = - 2 2 2 2 2 1 1 1 1 1 ( )( ) ( )( ) f i f i f i f i m v v v v m v v v v - + = - + 2 2 1 1 f i f i v v v v + = + 1 2 2 1 i i f f v v v v - = - Speed of approach = Speed of separation 1 1 2 2 1 1 2 2 f f i i m v m v m v m v + = + Momentum Conservation 1 1 1 1 2 2 2 2 1 1 2 2 1 1 2 2 2 2 2 2 f f i i m v m v m v m v + = + Energy Conservation 7

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October 24, 2010 Physics 131 - Lecture 17 Elastic Collisions We have two equations (conservation of momentum and conservation of kinetic energy) and two unknowns (the final speeds). Solving for the final speeds: 8
October 24, 2010 Physics 131 - Lecture 17 Three Elastic Collisions 1 2 1 1 2 2 ( ) ( ) ; fx ix m v v m m = + 1 2 1 1 1 2 ( ) ( ) fx ix m m v v m m - = + 1 2 2 1 1 : ( ) ( ) and ( ) (knock-o 0 n) fx ix fx m m v v v = = = 1 2 2 1 1 1 : ( ) 2( ) and (boost-ahe ( ) ( ) ad) fx ix fx ix m m v v v v = = 1 2 2 1 1 : ( ) 0 and ( ) ( ) (bounce-of f) fx fx ix m m v v v << = = - 9

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Elastic Collisions Consider a head-on, perfectly elastic collision of a ball of mass m 1 having initial velocity ( v i x ) 1 , with a ball of mass m 2 that is initially at rest. The solution, worked out in the text, is October 24, 2010 Physics 131 - Lecture 17 10
October 24, 2010 Physics 131 - Lecture 17 Example : Elastic Collision of Two Blocks A 4.0 kg block moving to the right at 6.0 m/s undergoes an elastic head-on collision with a 2.0 kg block moving to the right at 3.0 m/s.

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Physics131_L18WI10 - Physics 131 Mechanics Le cture18 Fe...

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