# M1 v1f m1 v1i m2 m2 v2i v v2f v so v1i

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Unformatted text preview: after. m1 v*1,f m1 v*1,i m2 m2 v*2,i v* v*2,f v* So |v*1,i - v*2,i| = |v*1,f - v*2,f| But the difference of two vectors is the same if we add the same constant to both (which is what you do if you view them in another reference frame). Rate of approach before an elastic collision is the same as the rate of separation afterward, in any reference frame! Physics 211 Lecture 13, Slide 5 Physics Act Consider the two elastic collisions shown below. In 1, a golf ball moving with speed V hits a stationary bowling ball head on. In 2, a bowling ball moving with the same speed V hits a stationary golf ball. In which case does the golf ball have the greater speed after the collision? A) 1 B) 2 B) C) same C) V 1 V 2 Physics 211 Lecture 13, Slide 6 Act A small ball is placed above a much bigger ball, and both are dropped together from a height H above the floor. Assume all collisions are elastic. What height do the balls bounce back to? H B A Before After C Physics 211 Lecture 13, Slide 7 Physics Explanation Explanation For an elastic collision, the rate of approach before is the same as the rate of separation afterward: v v 3v m m v M v v M v Rate of approach approach = 2V 2V Rate of Rate separation separation = 2V 2V Physics 211 Lecture 13, Slide 8 Physics Preflight A block slides to the right with speed V on a frictionless floor and collides with a bigger block which is initially at rest. After the collision the speed of both blocks is V/3 in opposite directions. Is the collision elastic? A) Yes B) No C) Need more information V V/3 Before Collision V/3 After Collision Physics 211 Lecture 13, Slide 9 Physics Is the collision elastic? A) Yes B) No C) Need more information V V/3 Before Collision V/3 After Collision A) both leave with same velocity B) In an elastic collision, the relative speeds of the blocks would be the same before and after the collision. Since this is not the case, this c...
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## This note was uploaded on 07/11/2012 for the course PHYS 211 taught by Professor Liss during the Spring '08 term at University of Illinois at Urbana–Champaign.

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