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 vmpdtpdamF)(12ttFJ)(1221ttFdtFJttxxx12ppJthen 0IfIFextPPF][FFIIBABAppppKEP&PPt1 t2 txFxF
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2 Many nuclear reactors use Li(M = 7mo) to moderate (reduce the KE) of neutrons (M n= mo) produced in nuclear reactions by elastic collisions with Linuclei.. An alternative is Na(M Na= 23mo). Liis a better choice because: A. Ptotis lower after nLicollision B. nhas less KEafter nLicollision compared to nNacollision C. Ptotis higher after nNacollision D. KEof ndoes not change after nNacollision E. Na is better choice (trick question) i-Clicker Li n Na n - or - Pfinal= Pinitial