Physics Homework
READ PAGES 34-37
Terms used to describe Physical Quantities
 Scalar quantities are numbers without any
direction
 Vector quantities that have both magnitude and
direction

If asked to determine the magnitude of a vector
quantity, just report a numeric answer
Motion
 Definition- the change in position or location of
an object


Motion is relative
must be described as it relates to a frame of reference

Examples: x – y plane
compass points
How far does an object move?
 Distance is a scalar quantity that describes total
length that an object has traveled from its origin
 Displacement is a change in position having both
magnitude and direction
 Equal

to the final position minus the initial position
Displacement = df - di
 Average velocity is a vector quantity describing the
time rate of change of the displacement of an object
 Average speed is the time rate of change in distance
of an object
 Scalar
Quantity
Avg velocity =
displacement
time
Units: meters/second (m/s)
A car traveling at 15 m/s speeds up at a constant rate
to 35 m/s over a 10 s time interval. What is the
average speed of the car during this time interval?
How far does this car travel during this time interval?
Acceleration
 Definition: the time rate of change of the velocity of
an object

Vector quantity
acceleration = change in velocity
time
a=DV
= Vfinal - Vinitial
t
t
Units: meters/ second2
Can the acceleration of an object be negative?
 What does it mean?
 Object is slowing down.
Do Now:
Homework:
A car traveling at 45 m/s
east is slowed uniformly
at a rate of 1.5 m/s2 for
10.0 s. What is the final
velocity of the car in
m/s?
 Answer questions on
pages:
64 #6, 7, 8, 10, 11
69 #26, 27, 29
How can we determine the displacement of an
object as it undergoes uniform acceleration?
 Equations can be derived by manipulating previously
learned equations.

Rearrange the average velocity equation to solve for d

When solving for the average velocity of an object when an
initial and final velocity are known we used the following
equation:
 We can substitute the equation for avg v into the
equation for d as follows:
 In the do now question the equation for acceleration
was rearranged to solve for Vf. Substitute this in for
the Vf in the equation we just determined and
combine like terms.
Practice
An airplane, starting from rest, undergoes an
acceleration of +3.0 m/s2 for 30.0 s before leaving
the ground. What is the airplane’s displacement
during this time interval?
Graphic Analysis of Displacement vs Time
Analyzing Distance vs Time Graphs
4
3
2
Displacement (m)
1
0
0
5
10
15
-1
-2
-3
-4
Time (s)
20
25
Graphic Analysis
Position versus time graphs:
- slope indicates the velocity (rate of change in
position) of the object
- Positive slope means object moves in a forward
direction
- Negative slope means object moves backwards
- No slope means object is at rest (not moving)
Do Now
 If the slope of a displacement vs time graph
represents velocity, what would a graph of
displacement vs time look like for an object that
undergoes uniform acceleration?
How can we determine the instantaneous velocity
of an object from a displacement vs time graph?
Graphical analysis of Constant Acceleration
Instantaneous
velocity – the speed and direction
that an object has at a particular point in time
140
120
Determining instantaneous velocity from a
displacement vs time graph
- identify the time in question
- draw a line tangent to the point
- determine the slope of the tangent line
Distance (m)
100
80
60
40
20
0
0
1
2
3
Time (s)
4
5
6
Do Now
 Using the instantaneous velocities previously
calculated, plot a graph of instantaneous velocity vs
time.

What is the relationship between the velocity and time for this
motion?
Does it look like this?
Analysis of Constant acceleration
60
50
Velocity (m/s)
40
30
20
10
0
0
1
2
3
time (s)
4
5
6
How can we determine the displacement of an
object from a velocity vs time graph?
 Identify the time interval in question
 Calculate the area under the graph.
 Determine the distance traveled by the object during
the first 3.0 seconds.
 Determine the distance traveled by the object from
2.0 to 4.0 seconds.