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Lect03

# Lect03 - Physics 112 Lecture 3 Todays Agenda q q Recap of...

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Physics 112: Lecture 3, Pg 1 Physics 112: Lecture 3 Physics 112: Lecture 3 Today’s Agenda Today’s Agenda Recap of 1-D motion with constant acceleration 1-D free fall example Motion in 2-D and 3-D: Strobe Diagrams vs position time graphs Review of Vectors

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Physics 112: Lecture 3, Pg 2 Review: Review: For constant acceleration we found: at v v 0 + = 2 0 0 at 2 1 t v x x + + = const a = x a v t t t v) (v 2 1 v ) x 2a(x v v 0 av 0 2 0 2 + = - = - From which we derived:
Physics 112: Lecture 3, Pg 3 1-D Free-Fall 1-D Free-Fall This is a nice example of constant acceleration (gravity): In this case, acceleration is caused by the “force of gravity”: MORE ON FORCES LATER Usually pick y-axis “upward” Acceleration of gravity is “down”: y a y = - g 2 y 0 0 t g 2 1 t v y y - + = y a v t t t g a y - = v y = v 0 y - g t

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Physics 112: Lecture 3, Pg 4 Gravity facts: Gravity facts: g does not depend on the nature of the material! Galileo (1564-1642) figured this out without fancy clocks & rulers! demo - freefall in vacuum Nominally, g = 9.81 m/s 2 At the equator g = 9.78 m/s 2 At the North pole g = 9.83 m/s 2 More on gravity in a few lectures! Freefall in vacuum This course: g = 9.8 m/s 2
Physics 112: Lecture 3, Pg 5 Problem: Problem: The pilot of a hovering helicopter drops a lead brick from a height of 1000 m. How long does it take to reach the ground and how fast is it moving when it gets there? (neglect air resistance) 1000 m

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Physics 112: Lecture 3, Pg 6 Problem: Problem: First choose coordinate system. Origin and y -direction. Next write down position equation: Realize that v 0y = 0 .
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