L12F11 - P123 F11 Lecture 12 18 Nov 2011 CENTER OF MASS...

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1 P123 F11 Lecture 12 18 Nov 2011 CENTER OF MASS MOTION & ROTATIONAL KINEMATICS REVIEW • LINEAR MOMENTUM: • IMPULSE OF A FORCE: (Strong force acting for short time) • Impulse-Momentum Theorem • CONSERVATION OF LINEAR MOMENTUM: • TYPES OF COLLISIONS: • LINEAR MOMENTUM CONSERVED IN COLLISIONS (When collision force >> external force) Elastic: conserved Inelastic: only is conserved Completely Inelastic: only conserved & objects stick v m p dt p d a m F ) ( 1 2 t t F J ) ( 1 2 2 1 t t F dt F J t t x x x 1 2 p p J then 0 If I F ext P P F ] [ ] [ F F I I B A B A p p p p KE P P P t 1 t 2 t x F x F
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2 Many nuclear reactors use Li ( M = 7 m o ) to moderate ( reduce the KE ) of neutrons ( M n = m o ) produced in nuclear reactions by elastic collisions with Li nuclei. . An alternative is Na ( M Na = 23 m o ). Li is a better choice because: A. P tot is lower after n Li collision B. n has less KE after n Li collision compared to n Na collision C. P tot is higher after n Na collision D. KE of n does not change after n Na collision E. Na is better choice (trick question) i-Clicker Li n Na n - or - P final = P initial
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3 CENTER OF MASS Point in an extended mechanical system that moves as though all the mass were concentrated at that point Consider a collection of (different) masses distributed on x-axis. Define center of mass: ... ... 3 2 1 3 3 2 2 1 1 m m m x m x m x m x cm i.e.: Similar expression for and If mass is a continuous distribution: cm y cm z M x m m x m x i i i i i cm i i i M r m r i i cm i dm r r M cm 1
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This note was uploaded on 01/03/2012 for the course PHYSICS 750:123 taught by Professor Ronaldgilman during the Fall '11 term at Rutgers.

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L12F11 - P123 F11 Lecture 12 18 Nov 2011 CENTER OF MASS...

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