ConcepTest 3.1
Relative Position
Three cars in the interchange depicted below all have the same
speed. Which pair has the greatest relative speed?
1)
2)
3)
4)
5)
Red and green
Red and blue
Green and blue
The relative speeds for all three
pairs are the same
More information about the
distances is necessary
ConcepTest 3.1
Relative Position
Three cars in the interchange depicted below all have the same
speed. Which pair has the greatest relative speed?
1)
2)
3)
4)
5)
Red and green
Red and blue
Green and blue
The relative speeds for all three
pairs are the same
More information about the
distances is necessary
ConcepTest 3.2
Relative Velocity
An automobile is moving toward the east at 30 mph on a day when
the wind is from the north at 30 mph. Which vector A, B, C, …
shown best represents the wind velocity as observed by a person
in the car?
ConcepTest 3.2
Relative Velocity
An automobile is moving toward the east at 30 mph on a day when
the wind is from the north at 30 mph. Which vector A, B, C, …
shown best represents the wind velocity as observed by a person
in the car?
Vwp = Vwe + Vep
Vwp = Vwe - Vpe
Vwp
-Vpe
Vwe
+Vpe
ConcepTest 3.3
Acceleration
From point P to R a rocket follows the path below. The speed of
the rocket triples over the course of the path. Which of the vectors
depicted could represent its acceleration at point Q?
ConcepTest 3.3
Acceleration
From point P to R a rocket follows the path below. The speed of
the rocket triples over the course of the path. Which of the vectors
depicted could represent its acceleration at point Q?
Don’t forget that the rocket
has both tangential and
centripetal acceleration.
ConcepTest 4.1 Newton’s Laws
You put your book on a
very greasy bus seat
next to you. When the
1) a net force acted on it
2) no net force acted on it
bus stops suddenly,
3) it remained at rest
the book slides forward
4) it did not move, but only seemed to
off the seat
seat. Why?
5) gravity briefly stopped acting on it
ConcepTest 4.1 Newton’s Laws
You put your book on a
very greasy bus seat
next to you. When the
1) a net force acted on it
2) no net force acted on it
bus stops suddenly,
3) it remained at rest
the book slides forward
4) it did not move, but only seemed to
off the seat
seat. Why?
5) gravity briefly stopped acting on it
The book was initially moving forward (since it was
on a moving bus). When the bus stopped, the book
continued moving forward,
forward which was its initial state
of motion,
motion and therefore it slid forward off the seat.
Follow--up: What is the force that usually keeps the book on the seat?
Follow
ConcepTest 4.2 Truck on Frozen Lake
A very large truck sits on a
frozen lake. Assume there is
no friction between the tires
and the ice
ice. A fly suddenly
smashes against the front
window. What will happen to
the truck after the fly
smashes into it?
1) it is too heavy, so it just sits there
2) it moves backward at const. speed
3) it accelerates backward
4) it moves forward at const. speed
5)) it accelerates forward
ConcepTest 4.2 Truck on Frozen Lake
A very large truck sits on a
frozen lake. Assume there is
no friction between the tires
and the ice
ice. A fly suddenly
smashes against the front
window. What will happen to
the truck after the fly
smashes into it?
1) it is too heavy, so it just sits there
2) it moves backward at const. speed
3) it accelerates backward
4) it moves forward at const. speed
5)) it accelerates forward
When the fly hit the truck, it exerted a force on the truck
(only for a fraction of a second). So, in this time period,
the truck accelerated (backwards) up to some speed.
After the fly was squashed, it no longer exerted a force,
and the truck simply continued moving at constant speed.
Follow--up: What is the truck doing 5 minutes after the fly hit it?
Follow
Two books are placed on Dr. Suess’s hand as shown below. The top book is
labeled 1 and the bottom book is labeled 2. The hand is accelerating the books
upward.
1 Physics 101 2 Physics 102 Which of the following Free-Body-Diagrams
(FBD) most accurately represents the forces
acting on book 1?
1)
2)
3)
4)
More than one FBD
are accurate.
5)
No FBD is accurate.