Transcript Lecture powerpoint

PHY 2048C
General Physics I with lab
Spring 2011
CRNs 11154, 11161 & 11165
Dr. Derrick Boucher
Assoc. Prof. of Physics
Sessions 6-7, Chapter 7
Chapter 6. Clicker Questions
A Martian lander is approaching the surface.
It is slowing its descent by firing its rocket
motor. Which is the correct free-body
diagram for the lander?
An elevator that has descended from the
50th floor is coming to a halt at the 1st
floor. As it does, your apparent weight is
A.
B.
C.
D.
less than your true weight.
equal to your true weight.
more than your true weight.
zero.
The terminal speed of a Styrofoam ball is 15
m/s. Suppose a Styrofoam ball is shot
straight down with an initial speed of
30 m/s. Which velocity graph is correct?
Chapter 7. Newton’s Third Law
Topics:
• Interacting Objects
• Analyzing Interacting Objects
• Newton’s Third Law
• Ropes and Pulleys
• Examples of Interacting-Object
Problems
Interacting Objects
If object A exerts a force on object B, then object B
exerts a force on object A. The pair of forces, as
shown, is called an action/reaction pair.
EXAMPLE 7.3 The forces on
accelerating boxes
EXAMPLE 7.3 The forces on
accelerating boxes
EXAMPLE 7.3 The forces on
accelerating boxes
EXAMPLE 7.3 The forces on
accelerating boxes
Example, Problem 7-30, p. 206
Example, Problem 7-32, p. 207
Chapter 7. Summary Slides
General Principles
General Principles
Important Concepts
Important Concepts
Applications
Applications
Chapter 7. Clicker Questions
Car B is stopped for a red light. Car A, which has
the same mass as car B, doesn’t see the red light
and runs into the back of B. Which of the
following statements is true?
A. A exerts a larger force on B than B exerts on A.
B. A exerts a force on B but B doesn’t exert a force
on A.
C. B exerts a force on A but A doesn’t exert a force
on B.
D. B exerts a larger force on A than A exerts on B.
E. B exerts the same amount of force on A as A
exerts on B.
Boxes A and B are sliding to the right across a
frictionless table. The hand H is slowing them
down. The mass of A is larger than the mass of B.
Rank in order, from largest to smallest, the
horizontal forces on A, B, and H.
A.
B.
C.
D.
FH on B = FH on A > FA on B
FB on H = FH on B = FA on B = FB on A
FB on H = FH on B < FA on B = FB on A
FB on H = FH on B > FA on B = FB on A
All three 50 kg blocks are at rest. Is
the tension in rope 2 greater than,
less than, or equal to the tension in
rope 1?
A. Equal to
B. Greater than
C. Less than
In the figure to the right,
is the tension in the
string greater than, less
than, or equal to the
weight of block B?
Assume that the system
is free to move.
A. Equal to
B. Greater than
C. Less than
A small car is pushing a
larger truck that has a
dead battery. The mass
of the truck is larger than
the mass of the car.
Which of the following statements is true?
A. The truck exerts a larger force on the car than the car exerts on the truck.
B. The truck exerts a force on the car but the car doesn’t exert a force on the
truck.
C. The car exerts a force on the truck but the truck doesn’t exert a force on the
car.
D. The car exerts a larger force on the truck than the truck exerts on the car.
E. The car exerts the same amount of force on the truck as the truck exerts on
the car.
The propulsion force on a car is due to
A. static friction.
B. kinetic friction.
C. the car engine.
D. elastic energy.
Is the tension in rope 2 greater than, less
than, or equal to the tension in rope 1?
A. greater than rope 1
B. less than rope 1
C. equal to rope 1
Chapters 7
Practice Problems
Chap 7: 21, 27, 31, 33, 35, 41
Unless otherwise indicated, all practice
material is from the “Exercises and Problems”
section at the end of the chapter. (Not
“Questions.”)