Physics 108 lecture 3: Velocity and Acceleration

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Physics 108 lecture 3 Velocity and Acceleration

• Speed and Velocity (recall distance divided by
  time)

Speed scalar magnitude only
Velocity vector magnitude direction
Units meters per second m/s
On the difference between speed and velocity
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• Example (Speed and Velocity) A car travels on a
  city grid as shown . Find
• Average speed
• Average velocity East
• Average velocity North
• Average velocity Northeast

Given                   
Path                Want     Conversions/Equations
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Acceleration

• A change in speed or velocity with time is
  acceleration
•  
• Vector magnitude and direction
• Units m/s2 (read as m per s squared or m
  per s per s)
• Value on surface of earth g _____________
• Equations

Relating acceleration, velocity, and time
Relating distance, acceleration, and time
If x0 0, v0 0 and t0 0, then simplify
If v0 0 and t0 0, then simplify
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Projectile Motion

• Projectile motion operates under two types of
  motion superimposed on each other               
  1) constant velocity in the x-direction
  (horizontal)                            object
  moves uniformly                2) constant
  acceleration due to gravity in the y-direction
  (vertical)                            object
  slows down as it goes up                         
     object speeds up as it goes down    - The
  two-dimensional shape of projectile motion is a
  parabola.    - The maximum range of a projectile
  occurs at an initial angle of 45.

y
Constant Acceleration
x
Constant speed
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Example (Projectile Motion) A package is to be
dropped over the edge of a bridge from a moving
car into a stationary boat waiting at the edge of
the shore below.  The car is traveling at 60 km/h
and the bridge is 25 m above the boat. a) how
long will it take for the package to fall into
the boat? b) how far from the end of the bridge
should the package be dropped?
Given                   
Path                Want     Conversions/Equations
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Summary of Motion