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Instructor’s informal sessions:

• Tuesday 3:30-4:20, WAG 420
• Friday 4-5pm, RLM4.102.

Lecture 23: Chapter 11 – Collisions-I

• Impulse: Time integral over force
• Conservation of momentum in a collision
• Elastic head-on collisions:

o General formula: v_i’-2v_cm-v_i, i=1,2

o Special case: m1=m2=m, v1=v0

• Derive (1).

o From velocity in lab to velocity in cm: v* = v - v_cm

o From velocity in cm to velocity in lab: v = v*+v_cm

o An elastic bounce in cm frame: v1*’= - v1* …

Reminders:

• Read chapter 11, begin on HW9.
• Attend Tuesday informal session, if you can.

Your exam letter grade: Determine two letter-grades you have made.

1. The “letter grade” based on the percent-score-cutoffs,

which are: 40%, 55%, 75% and 90% for D, C, B and A respectively;

2. The “letter-grade prime” based on scaled-score-cutoffs

which are: 400, 450, 525, and 600 for D, C, B and A respectively.

If the two letter-grades are not the same, the better is the one you have made.