PHYSICS 103: Lecture 3

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PHYSICS 103 Lecture 3
Agenda for Today

• Motion under uniform acceleration
• Freely falling objects
• Acceleration due to gravity
• Tracking a falling object

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Description of Motion with Uniform Accleration
Remember from last class that acceleration is
If a is constant
Where
v final velocity v0 initial velocity
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Example of Uniform Accleration
A car accelerates at 3 m/s2 from rest. What is
the final velocity after 20 seconds?
We know
v00 m/s
a3 m/s2
t20 s
How far did it travel in this time?
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Remember from last class that distance is
If acceleration, a, is constant, then
If acceleration, a, is constant, then the final
velocity, v, is given by
so
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Motion with Uniform Acceleration
When an object accelerates at a constant rate the
following applies
v vo at
acceleration
Final velocity
Initial velocity velocity at t 0
d d0 v0t 1/2at2
acceleration
Initial velocity velocity at t 0
Initial distance at t 0
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Example Problems for Uniform Accleration
1) A car starts out at a velocity of 2 m/s. If
it's acceleration is 3 m/s2, how fast will it be
going in 20 s?
2) A car starts out at a velocity of 2 m/s. If
it's acceleration is 3 m/s2, how long will it
take before it will be going 62 m/s
3) In the problem above, how far will it have
traveled?
4)A car starts out at a velocity of 2 m/s. If its
acceleration is 3 m/s2, how long will it take the
car to travel 640 m?
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Freely falling objects
Observations
1) Heavy objects and light objects fall at the
same rate with no air resistance
2) Things fall faster and faster until they hit
the ground (acceleration)
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Acceleration due to Gravity
Free-fall is an example of motion with uniform
acceleration
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A ball is dropped from a a tall building.How
long does it take to reach the ground? How fast
is it going?
where h 1224 ft 373 m to 102nd floor
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Example of free-fall
v vo at
d d0 v0t 1/2at2
d373 m
d00 m
v00 m/s
v vo at 0 (10m/s2)(8.64s) 86.4m/s
86.4 m/s (1/1000 km/m)(1/1.61 mile/km)(3600
s/hr)
193 mph
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Main Points from Todays Lecture

• Motion with Uniform (Constant) Acceleration

v vo at
acceleration
Initial velocity velocity at t 0
Final velocity
d d0 v0t 1/2at2
acceleration
Initial distance at t 0
Initial velocity velocity at t 0

• Free fall

• How long does it take to drop things
• How fast are they going at any given time?

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HW

• Re-Read Ch 3
• Make sure you understand all example problems
  done in class