PHY221 Ch13: Collisions, Impulse and Ref. Frames

1. Recall main points: A. Speed relation for elastic collisions. Helps solve some problems:

B. Definition of impulse and average force on one of the objects during any collision:

C. General expression for Kinetic energy:

2. Discussion and examples• Nothing special

PHY221 Ch13: Collisions, Impulse and Ref. Frames1.

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Proof: relative speed remains the same before /after collision:

PHY221 Ch13: Collisions, Impulse and Ref. Frames1.

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Impulse definition and expression in terms of average force on object during collision

PHY221 Ch13: Collisions, Impulse and Ref. Frames1.

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Proof: Kinetic Energy expression:(F=lab for instance) /

2/ /

12 CM FSYS F SYS CMK K MV

Prelim #1: * 0i imv

Prelim #2 for any mass mi : */ / / /i F i CM CM F i CM Fv v v v v

Now we compute 2/ / / /

1

2

1

2( )SYS F i i F i i F i FK mv m v v

PHY221 Ch13: Collisions, Impulse and Ref. FramesEX

ERCI

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