Physics 151 Week 3 Day 2

Topics– Motion Diagrams & Motion Graphs– Motion Definitions– Velocity to position– Adding and Subtracting Vectors Graphically

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.

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.

Checking Understanding 1Two runners jog along a track. The positions are shown at 1 s time intervals. Which runner is moving faster?

Slide 1-21

Two runners jog along a track. The positions are shown at 1 s time intervals. Which runner is moving faster?

Answer

A

Slide 1-22

Representations of Motion

Slide 2-9

Motion diagram (student walking to school)

Table of data Graph

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?

Checking Understanding 2

A.

Slide 2-13

B. C. D.

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?

Slide 2-14

C.

Answer

Checking Understanding 3

Slide 2-15

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 2-16

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.

Answer

Acceleration

Acceleration is:

• The rate of change of velocity

• The slope of a velocity-versus-time graph

Slide 2-20

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. Describe the motion of the ball as it moves from left to right2. Determine the average velocity of the ball from t = 2.1 s to t = 3.6 s.3. Determine the average speed of the ball from t = 0.6 s to t = 5.1 s.4. 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).

Ball on Ramps (From an Exam)

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

4. Velocity vectors point

A. in the same direction as displacement vectors.

Slide 1-9

Answer

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

Slide 1-7

Adding Vectors

Find the following resultants graphically

Vector Subtraction

Slide 3-10

Slide 3-11

Acceleration Vectors

Checking Understanding

Slide 3-13

Which of the vectors below best represents the vector sum P + Q?

Slide 3-14

Which of the vectors below best represents the vector sum P + Q?

Answer

Checking Understanding

Slide 3-15

Which of the vectors below best represents the difference P – Q?

Slide 3-16

Which of the vectors below best represents the difference P – Q?

Answer

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.

• 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.

Ball on Ramps (From an Exam)

QuickTime™ and a decompressor

are needed to see this picture.

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