Transcript 1 2 Re-Test Review File

1.2 Newton’s Laws Re-test
Review
Grab your journals. Find a partner or
group of 3 and sit together with your
journals out.
An elevator suspended by a vertical cable
is moving downward but slowing down.
The tension of the cable must be
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• An elevator suspended by a vertical cable is
moving downward but slowing down. The
tension of the cable must be
a. Less than the weight of the elevator
b. Greater than the weight of the elevator
c. Equal to the weight of the elevator
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is……B
1. Draw a free body diagram!!!!
2. Because the elevator is slowing down, you
know the FT has to be greater than Fg
An object of weight W is in freefall
close to the surface of Earth. The
magnitude of that force that the
object exerts on Earth is
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• An object of weight W is in freefall close to the
surface of Earth. The magnitude of that force
that the object exerts on Earth is
a.
b.
c.
d.
Zero
Less than W
Greater than W
Equal to W
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is…..D
1. Remember, magnitude is just a number, this
question is talking about the FORCE
2. Newton’s 3rd law states for every action force
there is an equal and opposite reaction force
3. The force is equal between the object and
Earth, but opposite in direction
An object of mass m rests on a flat
table. The earth pulls on this object
with a force of magnitude mg. What is
the reaction force to this pull?
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• An object of mass m rests on a flat table. The
earth pulls on this object with a force of
magnitude mg. What is the reaction force to this
pull?
a. The object pushing down on the table with force mg
b. The object pulling upward on the Earth with force
mg
c. The table pushing up on the object with force mg
d. The table pulling upward on the Earth with force mg
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is….B
1. Identify the two objects (object and Earth)
2. The question states Earth pulls on the object
3. Switch out your objects so your reaction
force will be the object pulls on Earth
4. We know gravity pulls down, so the opposite
force should be pulling up
A fireman is sliding down a fire pole. As he
speeds up, he tightens his grip on the pole,
thus increasing the vertical force that the
pole exerts on the fireman. When the force
on his hands equals his weight, what
happens to the fireman?
• In your journal, explain what this question is
asking, what concepts you need to understand to
answer this question, and what your answer to
this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with the
multiple choice below
• A fireman is sliding down a fire pole. As he speeds up,
he tightens his grip on the pole, thus increasing the
vertical force that the pole exerts on the fireman. When
the force on his hands equals his weight, what happens
to the fireman?
a. The fireman descends with a smaller but non-zero
acceleration
b. The fireman continues to descend, but with constant speed
c. The fireman descends with slower and slower speed
d. The fireman comes to a stop
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is….B
1. Draw a free body diagram!!!!!
2. If the vertical frictional force equals his
weight, his net force equals zero
3. If net force equals zero, then the he has no
acceleration and his speed is constant
A person is using a rope to lower a
5.0 N bucket into a well with a
constant speed of 2.0 m/s. What is
the magnitude of the force exerted
by the rope on the bucket?
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original owners
and answer the question with the multiple
choice below
• A person is using a rope to lower a 5.0 N
bucket into a well with a constant speed of 2.0
m/s. What is the magnitude of the force
exerted by the rope on the bucket?
a.
b.
c.
d.
10 N
0.00 N
5.0 N
49 N
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is…. C
• Newton’s 3rd law (for every action force, there is
an equal and opposite reaction force)
• The bucket is exerting a 5.0 N force on the rope
• So the rope must be exerting an equal and
opposite force on the bucket….which would be
5.0 N
• If it had asked about NET force, the answer would
have been 0.00 N because it is moving at
constant speed.
A person who normally weighs 700 N is
riding in an elevator that is moving
upward, but slowing down at a steady
rate. If this person is standing on a
bathroom scale inside the elevator, what
would the scale read?
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original owners
and answer the question with the multiple
choice below
• A person who normally weighs 700 N is riding in an
elevator that is moving upward, but slowing down at
a steady rate. If this person is standing on a bathroom
scale inside the elevator, what would the scale read?
a.
b.
c.
d.
700 N
Less than 700 N
More than 700 N
It could be more or less than 700 N, depending on
whether the magnitude of the acceleration is greater
than or less than 9.8 m/s2
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is …… B
1. Draw a free body diagram!!!!
2. Because the elevator is slowing down, the
acceleration must be negative (towards the
downward direction)
3. That means net force must be negative
(towards the downward direction)
4. Fnet = ΣF
A block is on a frictionless table on earth.
The block accelerates at 5.3 m/s2 when a
10 N horizontal force is applied to it. The
block and table are set up on the Moon,
where the acceleration due to gravity is
1.62 m/s2. A horizontal force of 5 N is now
applied to the block when it is on the
Moon. The acceleration imparted to the
block by this force is closest to
• In your journal, explain what this question is asking,
what concepts you need to understand to answer this
question, and what your answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original owners
and answer the question with the multiple
choice below
• A block is on a frictionless table on earth. The block
accelerates at 5.3 m/s2 when a 10 N horizontal force
is applied to it. The block and table are set up on
the Moon, where the acceleration due to gravity is
1.62 m/s2. A horizontal force of 5 N is now applied
to the block when it is on the Moon. The
acceleration imparted to the block by this force is
closest to
a. 3.2 m/s2
c. 2.7 m/s2
b. 2.4 m/s2
d. 2.9
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is ….. C
1. Acceleration due to gravity is extra
information
2. You know that the Force on Earth is 10 N,
then the force on the moon is 5 N
3. Force and acceleration are directly
proportional
4. If the force is halved, then the acceleration
must also half
On its own, a tow truck has a maximum
acceleration of 3.0 m/s2. What will be its
maximum acceleration when the truck is
using a light horizontal chain to tow a bus
of twice its own mass?
• In your journal, explain what this question is
asking, what concepts you need to understand
to answer this question, and what your
answer to this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• On its own, a tow truck has a maximum
acceleration of 3.0 m/s2. What will be its
maximum acceleration when the truck is using a
light horizontal chain to tow a bus of twice its
own mass?
a.
b.
c.
d.
2.0 m/s2
1.0 m/s2
1.5 m/s2
2.5 m/s2
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is….. B
1. F = ma
2. If you keep the force the same, and increase
the mass, you would have to decrease the
acceleration
3. Because you are adding a bus 2x the mass of
the tow truck, the total mass of the tow truck
with the bus is 3
4. If the mass increase by 3, the acceleration
would have to decrease by 3
A truck is moving at constant velocity.
Inside the storage compartment, a
rock is dropped from the midpoint of
the ceiling and strikes the floor
below. The rock hits the floor…
• In your journal, explain what this question is asking,
what concepts you need to understand to answer
this question, and what your answer to this question
is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• A truck is moving at constant velocity. Inside
the storage compartment, a rock is dropped
from the midpoint of the ceiling and strikes
the floor below. The rock hits the floor…
a.
b.
c.
d.
Behind the midpoint of the ceiling
Exactly below the midpoint of the ceiling
Ahead of the midpoint of the ceiling
More information is needed to solve this
problem
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is ….. B
• The truck is at constant velocity
• Everything on the truck is moving at constant
velocity
• The same velocity as the truck
• If something falls from the ceiling, it’s all going
the same speed and its within the system so it
hits the floor directly below from where it fell.
A sheet of paper can be withdrawn
from under a container of milk
without toppling it if the paper is
jerked quickly. This best demonstrates
that….
• In your journal, explain what this question is
asking, what concepts you need to understand to
answer this question, and what your answer to
this question is.
Swap your journal with your partner,
or within your group of 3
• Provide feedback to this person. Are they
understanding what the question is asking, do
they know what concepts are used to answer
this question and did they answer this
correctly or how you answered.
Swap journals back to their original
owners and answer the question with
the multiple choice below
• A sheet of paper can be withdrawn from
under a container of milk without toppling it if
the paper is jerked quickly. This best
demonstrates that….
a.
b.
c.
d.
The milk carton has inertia
The milk carton has inertia
Gravity tends to hold the milk carton secure
There is an action-reaction pair of forces
In your group (partnership) discuss…
• What did you miss?
• What did you do right?
• What did you do wrong?
And the answer is…. B
• Remember!!! Inertia is the resistance to
change
• The milk carton is at rest and wants to stay at
rest
• Even though the paper is being yanked out
from under the carton, the carton wants to
keep is the same spot