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. Description of Motion with Uniform Accleration. Remember from last class that acceleration is:. If a is constant:. Where:.

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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

Description of Motion with Uniform Accleration

Remember from last class that acceleration is:

If a is constant:

Where:

v = final velocity

v0 = initial velocity

Example of Uniform Accleration:

A car accelerates at 3 m/s2 from rest. What is the final velocity after 20 seconds?

We know:

v0=0 m/s

a=3 m/s2

t=20 s

How far did it travel in this time?

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:

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

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?

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)

Acceleration due to Gravity

Free-fall is an example of motion with uniform acceleration

initial

final

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

0

0

initial

final

Example of free-fall:

v= vo + at

d = d0 + v0t + 1/2at2

d=373 m

d0=0 m

v0=0 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

Main Points from Today’s Lecture

• Motion with Uniform (Constant) Acceleration

v= vo + at

acceleration

Final velocity

Initial velocity: velocity at t = 0

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?