Physics 151 Week 3 Day 2
Topics
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Motion Diagrams & Motion Graphs
Motion Definitions
Velocity to position
Adding and Subtracting Vectors Graphically
Where’s the train?
A train is moving at a steady 30 m/s. At t = 0, the engine
passes a signal light at x = 0. Without using any formulas,
find the engine's position at t = 1s, 2s, and 3s.
Express your reasoning in words.
Slide 2-34
Where’s the train?
A train is moving at a steady 30 m/s. At t = 0, the engine
passes a signal light at x = 0. Without using any formulas,
find the engine's position at t = 1s, 2s, and 3s.
Express your reasoning in words.
EQUATION FROM GRAPH
EQUATION FROM AREA
Slide 2-34
Checking Understanding 1
Two runners jog along a track. The positions are shown at 1 s
time intervals. Which runner is moving faster?
Slide 1-21
Answer
Two runners jog along a track. The positions are shown at 1 s
time intervals. Which runner is moving faster?
A
Slide 1-22
Representations of Motion
Motion diagram (student walking to school)
Table of data
Graph
Slide 2-9
Checking Understanding 2
Here is a motion diagram of a car moving along a straight stretch
of road:
Which of the following velocity-versus-time graphs matches this
motion diagram?
A.
B.
C.
D.
Slide 2-13
Answer
Here is a motion diagram of a car moving along a straight stretch
of road:
Which of the following velocity-versus-time graphs matches this
motion diagram?
C.
Slide 2-14
Checking Understanding 3
A graph of position versus time for a
basketball player moving down the
court appears like so:
Which of the following velocity graphs matches the above
position graph?
A.
B.
C.
D.
Slide 2-15
Answer
A graph of position versus time for a
basketball player moving down the
court appears like so:
Which of the following velocity graphs matches the above
position graph?
C.
Slide 2-16
Acceleration
Acceleration is:
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The rate of change of
velocity
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The slope of a velocityversus-time graph
Slide 2-20
Ball on Ramps (From an Exam)
A ball is released from rest at the point shown on the incline and speeds up. It
then rolls onto a level section of track at constant speed, and then rolls onto a
second incline with the same slope as the first where it slows down. The diagram
below shows the location of the ball at several instants in time. NOTE: THIS IS
NOT A STROBE PHOTOGRAPH OR MOTION DIAGRAM.
1.
2.
3.
4.
Describe the motion of the ball as it moves from left to right
Determine the average velocity of the ball from t = 2.1 s to t = 3.6 s.
Determine the average speed of the ball from t = 0.6 s to t = 5.1 s.
Determine the average acceleration, ax, of the ball as it goes up the 2nd
incline (from t = 3.6 s to t = 5.1 s).
Question
4. Velocity vectors point
A. in the same direction as displacement vectors.
B. in the opposite direction as displacement vectors.
C. perpendicular to displacement vectors.
D. in the same direction as acceleration vectors.
E. Velocity is not represented by a vector.
Slide 1-8
Answer
4. Velocity vectors point
A. in the same direction as displacement vectors.
Slide 1-9
Vectors
Slide 3-9
Adding Vectors Graphically
Slide 1-33
Adding Displacement Vectors
Slide 1-31
Example: Adding Displacement Vectors
Jenny runs 1 mi to the northeast, then 1 mi south.
Graphically find her net displacement.
Slide 1-32
Adding Vectors
Find the following resultants graphically
Slide 1-7
Vector Subtraction
Slide 3-10
Acceleration Vectors
Slide 3-11
Checking Understanding
Which of the vectors below best represents
the vector sum P + 
Q?
Slide 3-13
Answer
Which of the vectors below best represents
the vector sum P + 
Q?
Slide 3-14
Checking Understanding
Which of the vectors below best represents

the difference P– Q?
Slide 3-15
Answer
Which of the vectors below best represents

the difference P– Q?
Slide 3-16
Ball on Ramps (From an Exam)
A ball is released from rest at the point shown on the incline and speeds up. It
then rolls onto a level section of track at constant speed, and then rolls onto a
second incline with the same slope as the first where it slows down. The diagram
below shows the location of the ball at several instants in time. NOTE: THIS IS
NOT A STROBE PHOTOGRAPH OR MOTION DIAGRAM.
QuickTime™ and a
decompressor
are needed to see this picture.
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•
Draw a motion diagram for the following motion
On the diagram above, use a delta v diagram to help draw an arrow
indicating the direction of the acceleration of the ball at point A.
Example: Velocity Vectors
Jake throws a ball at a 60° angle, measured from the
horizontal. The ball is caught by Jim. Draw a motion diagram
of the ball with velocity vectors.
Slide 1-35