# 講者： 許永昌 老師 1. Contents 2 後面幾章的重點 Action: Law of Conservation of mass ( 請預讀 P239) Purpose: Realize the meaning of “conservation”. Realize the significance.

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Contents 2 後面幾章的重點

Action: Law of Conservation of mass ( 請預讀 P239) Purpose: Realize the meaning of “conservation”. Realize the significance of “before” and “after”. Action: Water + Juice  Drink Before: m water and m juice. After: m drink. Conservation: m water + m juice = m drink. 3

Momentum and Impulse ( 請預讀 P240~P247) 4 JxJx t(s) F x (N)

Action: Impulse 5

Example 9.1 A 150 g baseball is thrown with a speed of 20 m/s. It is hit straight back toward the pitcher at a speed of 40 m/s. The interaction force between the ball and the bat is shown in the graph. What maximum force F max does the bat exert on the ball? 6 t(s) F x (N) 6.0 ms F max

Student Workbook P9-3 A carnival game requires you to knock over a wood post by throwing a ball at it. You’re offered a very bouncy rubber ball and a very sticky clay ball of equal mass. Assume that you can throw them with equal speed and equal accuracy. You only get one throw. Which ball will you choose? Why? 7

Homework Student Workbook: 9.1 9.2 9.4 9.7 9.9 9.11 8

Summary I 9

Law of Conservation of Momentum ( 請預讀 P247~P252) System: Total Momentum: Net force: Newton’s 2 nd Law of Motion: For a System: 10 這就是為何我們常常 簡化問題為 particle 的 樣子。

Collisions ( 請預讀 P253~P255) 11

Explosions ( 請預讀 P255~P257) System: Fuel+Rocket Before: P i,y =(M+  m)v i,y. Final: P f,y =Mv f,y +  m(v f,y +v thrust,y ). We get: 12

Examples: Textbook: 9.45: An object at rest on a flat, horizontal surface explodes into two fragments, one seven times as massive as the other. The heavier fragment slides 8.2 m before stopping. How far does the lighter fragment slide? Assume that both fragments have the same coefficient of kinetic friction. A 10 g bullet is fired into a 1.0 kg wood block, where it lodges. Subsequently, he block slides 4.0 m across a floor (  k =0.20 for wood on wood). What was the bullet’s speed? 13

Homework Student Workbook: 9.14 9.16 9.20 Student Textbook: 9.25 9.30 9.41 一樣，請製作卡片。 14

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