Ian Torregrosa Newtons_Laws_Recovery_Grade_Assignment
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Sistema Universitario Ana G Mendez *
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2011
Subject
Physics
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Feb 20, 2024
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31
Uploaded by ntorregrosa4
Newton's Laws Name: Page 1 Newton
’
s Laws Work Instructions: This assignment is to give you the opportunity to make up your grade in class. Therefore, it must be completed in its entirety. You must SHOW ALL the WORK for those math problems that you will find in order to receive the credit for it. So, please read carefully and make sure you read and answer every question. Remember that if you do not remember the material you must do your own research about the topic to help you explain the answer. This assignment must be turned NO later than December 12
th
, 2023 Inertia and Mass 1.
Inertia
is
the tendency of objects in motion to stay in motion, and objects at rest to stay at rest, unless a
force causes its speed or direction to change.
2.
The amount of inertia possessed by an object is dependent solely upon its __
mass
________.
3.
Two bricks are resting on edge of the lab table. Shirley Sheshort stands on her toes and spots the two
bricks.
She acquires an intense desire to know which of the two bricks are most massive. Since Shirley is
vertically
challenged, she is unable to reach high enough and lift the bricks; she can however reach high
enough to give
the bricks a push. Discuss how the process of pushing the bricks will allow Shirley to
determine which of the
two bricks is most massive. What difference will Shirley observe and how can this
observation lead to the
necessary conclusion?
4.
Would Shirley Sheshort be able to conduct this same study if she was on a spaceship in a location in space far
from the influence of significant gravitational forces? _______ Explain your answer.
5.
If a moose were chasing you through the woods, its enormous mass would be very threatening. But if you
zigzagged, then its great mass would be to your advantage. Explain why.
6.
Inertia can best be described as _____.
a.
the force which keeps moving objects moving an stationary objects at rest.
b.
the willingness of an object to eventually lose its motion
c.
the force which causes all objects to stop
d.
the tendency of any object to resist change and keep doing whatever its doing
Ian Torregrosa
The brick with more mass will be more resistant to move. It has more inertia.
Yes, because Bricks that are harder to move has more inertia. Mass does not change. It have nothing to do with gravity
The moose has a lot of inertia so it would be harder for him to change direction.
Newton's Laws Page 2 7.
Mass and velocity values for a variety of objects are listed below. Rank the objects from smallest to greatest
inertia. ___
C
____ < ___
D
____ < ___
A
____ < ____
B
___
Pre-Conceptions Students typically have many pre-conceived notions regarding concepts in Physics. It has always proven useful to bring these ideas to the forefront of your mind and to make an effort to evaluate their correctness. The following statements pertain in one way or another to common notions regarding central concepts of this unit. Identify each statement as being either true (
T
) or false (
F
). Force and Motion - What Do You Believe? The following statements pertain in one way or another to common notions regarding force and motion. Identify each statement as being either true (
T
) or false (
F
). T or F? Statement 1.
A force is required to keep an object moving in a given direction.
2.
An upward moving object must be experiencing (or at least usually does experience) an
upward force.
3.
A rightward moving object must be experiencing (or at least usually does experience) a
rightward force.
4.
A ball is moving upwards and rightwards towards its peak. The ball experiences a force that is
directed upwards and rightwards.
5.
If a person throws a ball with his hand, then the force of the hand upon the ball is experienced
by the ball for at least a little while after the ball leaves the hand.
6.
A cannonball is shot from a cannon at a very high speed. The force of the explosion will be
experienced by the cannonball for several seconds (or a least a little while).
7.
If an object is at rest, then there are no forces acting upon the object.
F
F
F
F
F
F
F
Newton's Laws Name: Page 3 Mass and Weight - What Do You Believe? The following statements pertain in one way or another to common notions regarding mass and weight. Identify each statement as being either true (
T
) or false (
F
). T or F? Statement 1.
Objects do NOT weigh anything when placed in a vacuum.
2.
All objects weigh the same amount when placed in a vacuum, regardless of their mass.
3.
An object weighs less on the moon than it does on the Earth.
4.
The mass of an object on the moon is the same as its mass on the Earth.
5.
A high-speed object (say, moving at 200 mi/hr) will weigh less than the same object when at rest.
6.
A high-speed object (say, moving at 200 mi/hr) will possess measurably more mass than the
same object when at rest.
7.
Weight is measured in pounds; mass is measured in Newtons.
8.
A free-falling object still has weight.
9.
Weight is the result of air pressure exerted upon an object.
Balanced vs. Unbalanced Forces Review: An object at rest ... ; An object in motion ....
; unless ... . 1.
The amount of force required to keep a 6-kg object moving with a constant velocity of 2 m/s is __ N.
a. 0.333
b. 2
c. 3
d. 6
e. 12 f. ... nonsense! A force is NOT required to keep an object in
motion.
2.
Renatta Oyle is having car troubles. She is notorious for the trail of oil drops that she leaves on the streets of
Glenview. Observe the following oil traces and indicate whether Renatta's car is being acted upon by an
unbalanced force. Give a reason for your answers.
Unbalanced Force?
a. Reason: Yes or No
b. Reason: Yes or No
Ian Torregrosa
F
F
T
T
F
F
F
T
F
will stay at rest
will stay in motion
unless acted upon by an unbalanced force
The car is speeding up; the spacing between consecutive positions is
increasing
The car is moving at a constant speed; the spacing between consecutive
positions is constant
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Newton's Laws Page 4 c. Reason: Yes or No
3.
Each one of the dot diagrams in question #2 can be matched to a force diagram below. The force diagrams
depict the individual forces acting upon the car by a vector arrow. The arrow direction represents the
direction of the force. The arrow length represents the strength of the force. Match the dot diagrams from
#2 to a force diagram; not every force diagram needs to be matched.
Dot Diagram(s): ____
C
___
Dot Diagram(s): ____
A
___
Dot Diagram(s): __
B
_____
4.
If the net force acting upon an object is 0 N, then the object MUST _
E
___. Circle one answer.
a.
be moving
b.
be accelerating
c.
be at rest
d.
be moving with a constant speed in the same direction
e.
either c or d.
5.
These graphs describe the motion of Carson Busses at various times during his trip to school. Indicate
whether Carson's vehicle is being acted upon by an unbalanced force. Give a reason in terms of a description
of what the car is doing (speeding up, slowing down, or constant velocity).
Unbalanced Force? Yes or No? Unbalanced Force? Yes or No? Unbalanced Force? Yes or No? The car is slowing down; the spacing between consecutive positions is
decreasing.
No
Yes
Yes
Newton's Laws Name: Page 5 Reason/Description: Reason/Description: Reason/Description: 6.
A free-body diagrams show all the individual forces acting upon an object. The net force is the vector sum
of
all these forces (
∑
F). Determine the net force and state if there is an acceleration.
a. b. c. Accel'n? Yes or No Accel'n? Yes or No Accel'n? Yes or No 7.
During an in-class discussion, Anna Litical suggests to her lab partner that the dot diagram for the motion of
the object in #6b could
be
Anna's partner objects, arguing that the object in #6b could not have any horizontal motion if there are only vertical forces acting upon it. Who is right? _
Anna
___________ Explain.
8.
During an in-class discussion, Aaron Agin asserts that the object in #6a must
be moving to the left since the
only horizontal force acting upon it is a "left-ward" force. Is he right? _
No
_____ Explain.
9.
The diagrams below depict the magnitude and direction of the individual forces acting upon an object.
Which objects could be
moving to the right? Circle all that apply.
Ian Torregrosa
There is a constant velocity;
unbalanced forces change the velocity.
The is an acceleration; the
vehicle is slowing down. Unbalanced forces cause this.
There is an acceleration; the
vehicle is speeding up. Unbalanced forces cause this.
10 N, left
0 N
15 N, up
If horizontal forces are balanced, then there is no acceleration. There could however be a horizontal motion. The object
is either at rest (as Anna's partner insists) OR moving at a constant velocity.
Regrettably, Aaron believes that forces cause motion and a leftward force is consistent with a leftward motion. This thinking causes Isaac
Newton to roll over in his grave. The fact is that forces causes accelerations. The fact that the force is friction is an indicator that the object is probably moving to the right ans lsowing down, consistent with a leftward acceleration and leftward net force.
ABCDE Any of these objects could be moving to the right since a net force does not indicate which way an object is moving. Objects
D and E could be moving right and slowing down. Object A and B could be moving right at a constant speed. Object C could be moving right and speeding up.
Newton's Laws Page 6 Net Force Help Sheet Understanding the influence of individual forces upon the acceleration of objects demands familiarity with the variety of types of forces. Quickly internalize the following. Type of Force Explanation Weight (W) or Force of Gravity (Fgrav) The force of gravity
is the force at which the earth, moon, or other massively large object attracts another object towards itself. By definition, this is the weight
of the object. All objects upon earth experience a force of gravity which is directed "downward" towards the center of the earth. The force of gravity on earth is always equal to the weight of the object as found by the equation: Fgrav = m * g where g = 9.8 N/kg (on Earth)
Normal Force (Fnorm or FN) The normal force
is the support force exerted upon an object which is in contact with another stable object. For example, if a book is resting upon a surface, then the surface is exerting an upward force upon the book in order to support the weight of the book. On occasions, a normal force is exerted horizontally between two objects which are in contact with each other. Spring (Fspring or Fs) The spring force
is exerted by a spring upon the objects connected to each of its two ends. Spring forces may result from either a compressed or a stretched spring. The magnitude of a spring force is dependent upon the elasticity of the spring (usually denoted by its spring constant k
) and upon the amount of compression or stretch (
x
) of the spring from its equilibrium
position. The general equation for spring force is Fspring = k * x Sliding Friction Forces (Ffrict or Ff)
The frictional force
is the force exerted by a surface as an object moves across it. The sliding friction force opposes the motion of the object. For example, if a book moves across the surface of a desk, then the desk exerts a frictional force in the opposite direction of its motion. The frictional force can often be calculated using the equation: Ffrict = μ * Fnorm
Air Resistance (Fair or R) The air resistance
is a special type of frictional force which acts upon objects as they travel through the air. The force of air resistance always opposes the motion of the object. This force will frequently be neglected due to its negligible magnitude. It is most noticeable for objects which travel at high speeds (e.g., a skydiver or a downhill skier) or for objects with large surface areas.
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Newton's Laws Name: Page 7 Tension (Ftens or T) The tension
is the force which is transmitted through a string, rope, wire or cable when it is pulled tight by forces acting from each end. The tensional force is directed along the wire and pulls equally on the objects on either end of the wire. Applied Force (Fapp or Fa) The applied force
is the force which is applied to an object by a person or another object. If a person is pushing a desk across a room, then there is an applied force acting upon the object. The applied force is the force exerted on the desk by the person. The Net Force
The net force
is the vector sum of all the individual forces acting upon an object. In other words, Fnet = F1 + F2 + F3 + ... where F1, F2, and F3 represent the various forces acting upon an object. Like any force, the net force is a vector and has a direction. Being the vector sum of all the forces, there may be some negative signs present in the net force equation to indicate that one force is opposite in direction to another force. According to Newton's second law, the net force is related to mass and acceleration Fnet = ∑
F = m * a
Other Noteworthy Items: 1.
Scales
are devices which are equipped with springs that are compressed or stretched when objects are
placed upon the scales. These springs allow the scales to measure the magnitude of other forces (i.e., normal
forces, tensional forces, gravitational forces, etc.) acting upon the object.
2.
Pulleys
are objects which change the direction of a force but not its magnitude.
Problem-Solving Strategy: To solve problems involving several forces acting upon a single object: 1.
Sketch a free-body diagram (FBD). To simplify the diagram, represent the object by a "box". Draw arrows
representing all the forces acting on the object. The direction of each arrow should indicate the direction of
the force.
2.
Label each arrow on the FBD with a symbol to indicate the type of force it is. Use the table above to help you
label the forces appropriately.
3.
Write down all given information in variable form (e.g., m = 2.0 kg; a = 1.5 m//s, right). Write down the
desired end - what the problem asks to be determined or calculated (e.g., find Fapp).
4.
The net force is the vector sum of all the individual forces acting on the object. The "summing" of individual
forces is simplified if the horizontal and vertical forces are summed separately. Indicate this in the form of
equations based upon the FBD.
Ian Torregrosa
Newton's Laws Page 8 Horizontal ∑
Fx = Fright - Fleft (assumes that rightward is the + direction) Vertical ∑
Fy = Fup - Fdown (assumes that up is the + direction) 5.
Write the net force equations (
∑
Fx
= m * ax and ∑
Fy
= m * ay).
6.
Solve the problem for the desired information by relating the #4 and the #5 equations.
Perhaps the most difficult (and most critical) principle of mechanics is the principle of net force and acceleration. You will probably be tempted to approach Fnet problems in a memorization mode
. Avoid such an approach; nothing could lead you into a state of frustration more readily. Rather, internalize the meaning of the various forces, learn to recognize their presence by careful analysis of a problem, and base your problem-solving strategies on an understanding of such concepts and upon the application of good logic and reasoning. Approach Fnet problems in logic mode
. Recognizing Forces There are several situations described below. For each situation, fill in the list provided by indicating which forces are present and stating which features of the situation you used to determine the presence or absence of the force. To facilitate this exercise, utilize the Net Force Help Sheet. Upon completion of this assignment, check your answers using the available Web page.
Newton's Laws Name: Page 9 Ian Torregrosa
The force of gravity acts upon all objects;
the Earth and the object attract.
There are no springs touching the object;
thus, there is no spring force.
A taut rope is attached to the object; this is
the cause of the tension force
The block is not being directly supported
on any of its sides by a stable surface
The object is not moving across the surface
so it does not experience friction
If an object is not moving (relative to the]
surrounding air), then there is no F air
A stretched spring is attached to the block;
this is the cause of spring force
There are no strings (or ropes or ...)
connected to the object and pulled tight
The force of gravity acts upon all objects;
the Earth and the object attract.
The block is not being directly supported
on any of its sides by a stable surface
The object is not moving across the surface
so it does not experience friction
If an object is not moving (relative to the]
surrounding air), then there is no F air
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Newton's Laws Page 10 The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
There are no springs touching the ball in
the air; thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no strings (or ropes or ...)
connected to the object and pulled tight
There are no strings (or ropes or ...)
connected to the object and pulled tight
There are no strings (or ropes or ...)
connected to the object and pulled tight
The ball is not being supported on any of
its sides by a stable surface
The skydiver is not being supported on
any of its sides by a stable surface
The block is being directly supported by a
stable surface (the table)
The object is not moving across the surface
so it does not experience surface friction
The object is not moving across the surface
so it does not experience surface friction
The object is not moving or trying to move
across a surface so there is no F frict.
If an object is moving (through air), then there is a F air; it is often a small force
If an object is moving (through air), then
there is a F air.
If an object is not moving (relative to the]
surrounding air), then there is no F air
Newton's Laws Name: Page 11 Ian Torregrosa
If an object is moving (through air), then
there is a F air.
If an object is moving (through air), then there is a F air; it is often a small force
If an object is moving (through air), then there is a F air; it is often a small force
The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
There are no springs touching the object;
thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no strings (or ropes or ...)
connected to the object and pulled tight
There are no strings (or ropes or ...)
connected to the object and pulled tight
There are no strings (or ropes or ...)
connected to the object and pulled tight
Even when moving , the block is still being
directly supported by a stable force
Even when moving , the block is still being
directly supported by a stable force
Even when moving , the car is still being
directly supported by a road surface
The object is moving across a surface and
thus experience friction
The object is moving across a surface and
thus experience friction
As wheels turn, they grip the road due
to friction, resulting in a forward force
Newton's Laws Page 12 The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
The force of gravity acts upon all objects;
the Earth and the object attract.
There are no springs touching the object;
thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no springs touching the object;
thus, there is no spring force.
There are no strings (or ropes or ...)
connected to the object and pulled tight
There are no strings (or ropes or ...)
connected to the object and pulled tight
A taut rope is attached to the bucket; this is
the cause of the tension force
The person is still being directly supported
by the sled surface
The sled is slows down due to friction. The person
would slide forward across the seat if he did not experience friction as well
Even when moving , the car is still being
directly supported by the road surface
The wheels are skidding across the road and thus experiencing friction
The object is not being supported on any
of its sides by a stable surface
The object is not moving across a surface
so it does not experience surface friction
If an object is moving (through air), then
there is an F air.
If an object is moving (through air), then there is a F air; it is often a small force
If an object is moving (through air), then there is a F air; it is often a small force
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Newton's Laws Name: Page 13 Mass and Weight
1.
The standard metric unit for mass is _
kilogram
____ and the standard metric unit for weight is _
Newton
____.
2.
An object's mass refers to _
the amount of stuff present in the object
____ and an object's weight refers to _
the force of gravitational attraction to Earth
____. Fill in each blank.
a.
the amount of space it takes up
b.
the force of gravitational attraction to Earth
c.
how dense an object is
d.
the amount of stuff present in the object
3.
Complete the following table showing the relationship between mass and weight.
Object Mass Approx. Weight Melon 1 kg Apple ~1.0 N Pat Eatladee 25 kg 4.
Different masses are hung on a spring scale calibrated in Newtons.
The force exerted by gravity on 1 kg = ~10 N. The force exerted by gravity on 5 kg = ~__
50
____ N. The force exerted by gravity on 70 kg = ~__
700
___ N. 5.
The value of g in the British system is 32 ft/sec2. The unit of force is pounds. The unit of mass is the slug. Use
your weight in pounds to
calculate your mass in units of slugs. PSYW
6.
You might be wondering about your metric weight. Using conversion
factors, convert your weight in pounds to units of N. (Use 1 N = 0.22 pounds) PSYW
Ian Torregrosa
9.8 N
0.10 kg
245 N
(more precisely, 49 N)
(more precisely, 686 N)
Answers will vary. The calculation for a 160-pound person is:
Mass = Weight/g = (160 lbs)/(32 ft/s2) = 5.0 slug
Answers will vary. The calculation for a 160-pound person is:
160 lb . (1.0 N/0.22 lb) = 730 N (727.27 ... N)
Newton's Laws
Page 14 7.
What is the mass and weight of a 10-kg object on earth?
Mass = Weight = What is the mass and weight of a 10-kg object on the moon where the force of gravity is 1/6-th that of the Earth's? Mass = Weight = 8.
Conclusion: The __
mass
_____________ of an object is independent of the object's location in space.
Newton's Second Law of Motion
1.
The acceleration of an object is __
directly
__________________ related to the net force exerted upon it and
__
inversely
___________________ related to the mass of the object. In equation form: a = Fnet / m.
a.
directly, inversely
b.
inversely, directly
c.
directly, directly
d.
inversely, inversely
2.
Use Newton's second law to predict the effect of an alteration in mass or net force upon the acceleration of an
object.
a.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon
increased by a factor of 2. The new acceleration will be __
16
_______ m/s2.
b.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon increased by
a factor of 4. The new acceleration will be ___
32
______ m/s2.
c.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon
decreased by a factor of 2. The new acceleration will be ___
4
______ m/s2. d.
An object is accelerating at a rate of 8 m/s2 when it suddenly has its mass increased by a factor of 2. The
new acceleration will be ____
4
_____ m/s2.
e.
An object is accelerating at a rate of 8 m/s2 when it suddenly has its mass decreased by a factor of 4. The
new acceleration will be ___
32
______ m/s2.
10 kg
98 N (mass multiplied by 9.8)
10 kg
16 N (one-sixth of 98 N)
Newton's Laws Name: Page 15 f.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon increased by
a factor of 2 and its mass decreased by a factor of 4. The new acceleration will be __
64
_______ m/s2.
g.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon increased by
a factor of 4 and its mass increased by a factor of 2. The new acceleration will be ___
16
______ m/s2.
h.
An object is accelerating at a rate of 8 m/s2 when it suddenly has the net force exerted upon increased by
a factor of 3 and its mass decreased by a factor of 4. The new acceleration will be _____
96
____ m/s2.
3.
These force diagrams depict the magnitudes and directions of the forces acting upon four objects. In each
case, the down force is the force of gravity. Rank these objects in order of their acceleration, from largest to
smallest: ___
C
____ > ___
A
____ > ___
D
____ > ___
B
____
Net Force and Acceleration
Luke Autbeloe drops a 5.0 kg fat cat (weight = ~50.0 N) off the high dive into the pool below (which on this occasion is filled with water). Upon encountering the water in the pool, the cat encounters a 50.0 N upward
restraining force. Which one of the velocity-time graph best describes the motion of the cat? __
B
______ Accompany your answer with a description of the cat's motion. A
B
C
Description of cat's motion while falling through air: Description of cat's motion after hitting the water: Ian Torregrosa
Accelerating at -10m/s2
No net force, constant
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Newton's Laws
Page 16 1.
Which one of the following dot diagrams best describes
the motion of the falling cat from the time that they are
dropped to the time that they hit the ground? __
A
_____
The arrows on the diagram represent the point at which
the cat hit the water. Support your answer with sound
reasoning:
3 Several of Luke's friends were watching the motion of the falling cat. Being "physics types", they began discussing the motion and made the following comments. Indicate whether each of the comments are correct or incorrect? Support your answers. Correct? Student Statement:
Yes or No
a.
Once the cat hit the pool, the forces are balanced and the cat will stop.
Reason:
b.
Upon hitting the pool, the cat will accelerate upwards because the pool applies an
upward force.
Reason:
c.
Upon hitting the pool, the cat will bounce upwards due to the upwards force.
Reason:
Dots show larger gaps until hits water, then constant (gaps
same distance)
No FNET = NO
NO
NO
Upward = Downward, no fnet
same as b. remember fnet will give, not direction of movement
Newton's Laws Name: Page 17 4.
For each force diagram, determine the net or resultant force (
∑
F), the mass and the acceleration of the
object. Identify the direction (the second blank) of the two vector quantities. NOTE: Fgrav stands for the
weight of the object.
a. ∑
F = a = , m = , b. ∑
F = a = , m = , c. ∑
F = a = , m = , d. ∑
F = a = , m = , Ian Torregrosa
600 N
down
60 kg
10 m/s2
down
200 N
down
60 kg
3.33 m/s2
down
2,000 N
left
800 kg
2.5 m/s2
left
4,000 N
left
800 kg
5 m/s2
left
Newton's Laws Page 18 e. ∑
F = a = , m = , f. ∑
F = a = , m = , Free-Body Diagrams Construct free-body diagrams for the following physical situations. Label all forces (e.g, Fgrav, Fnorm, Fapp, Ffrict, Fair, Ftens, etc. ). a.
A physics book rests
upon a level table.
c. A sledder has reached the
bottom of a hill and is
coasting rightward while slowing down. b. The brakes are applied to a rightward moving car and it
skids to a stop.
d.
An elevator is rising at a constant velocity; it is not
touching the elevator shaft.
8 N
right
2 kg
4 m/s2
right
16 N
right
4 kg
4 m/s2
right
Fn - up
Fg - down
Fn - up
Fg - down
Ff - left
Normal, Friction left, gravity
Tension upward, gravity
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Newton's Laws Page 19 Newton's Second Law Free-body diagrams are shown for a variety of physical situations. Use Newton's second law of motion (
∑F=m•a) to fill in all blanks. Use the approximation that g = ~10 m/s/s. a. b. c. m=10000 kg m=800 kg a = 8.0 m/s/s, down a = 6.0 m/s/s, up S
F = ________
S
F = _
80000 N, down
__ d. e. f. g. h. i. S
S
0.01 kg
0 m/s2
0 N
2,000 N
100000
12800 n
8000 n
4800 N, up
1000 kg
9 m/s2, left
9000 N, left
5 N
124 N
5 N
248 m/s2
1350 N
900 kg
1350 N, right
Newton's Laws Page 20 Drawing Free Body Diagrams For the following situations, draw a free-body diagram in which you represent the various forces that are acting upon the object(s) using vector arrows. Label each arrow to indicate the type of force. Determine the magnitude of all forces and fill in the blanks. 1.
A 1.0 kg book is at rest on a tabletop. Diagram the forces acting on the book.
FBD: ∑
Fx = ∑
Fy = ax = ay = 2.
A 5.0 kg flying squirrel is flying from a tree to the ground at constant velocity. Consider air resistance.
Diagram the forces acting on the squirrel.
FBD: ∑
Fx = ∑
Fy = ax = ay = 3.
An egg with a weight of 0.10 N is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces
acting on the egg as it is falling.
S
150 N
7.5 N
150 N
7.5 N, right
60 kg
1.67 m/s2
100 N, left
2000 N
20000 N
4000, right
Newton's Laws Name: Page 21 FBD: ∑
Fx = ∑
Fy = ax = ay = A 2.0-kg bucket is tied to a rope and accelerated upward out of a well at a rate of 1.5 m/s/s. Neglect air resistance. Diagram the forces acting on the bucket. FBD: ∑
Fx = ∑
Fy = ax = ay = 4.
A 2.0-N force is applied to a 1.0 kg book in order to move it across a desk with an acceleration of 0.5 m/sec2.
Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book.
FBD: ∑
Fx = ∑
Fy = ax = ay = 5.
A 1.5-N force is applied to a 1.0 kg book in order to move it across a desk at constant velocity. Consider
frictional forces. Neglect air resistance. Diagram the forces acting on the book. FBD: ∑
Fx = ∑
Fy = ax = ay = Ian Torregrosa
FBD: Fx = Fy = 2.0 N, ax = 0.5 m/s^2.
FBD: Fx = Fy = 1.5 N, ax = 0 m/s^2.
Finet =(2,0)(1,5)=3 N
ε F+F ket =Fω+Ft
Mrode 3x=H/L+F
+19.6+115.6
22.6=7t
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Newton's Laws Page 22 6.
A 70.0-kg skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting
upon the skydiver.
FBD: ∑
Fx = ∑
Fy = ax = ay = 7.
A 30-N force is applied to drag a 20-kg sled across loosely packed snow with an acceleration of 1.0 m/s2.
Diagram the forces acting upon the sled.
FBD: ∑
Fx = ∑
Fy = ax = ay = 8.
An 800-kg car is coasting to the right with a leftward acceleration of 1 m/s2. Diagram the forces
acting upon the car.
FBD: ∑
Fx = ∑
Fy = ax = ay = Friction 1.
A classroom desk supported by long legs is stationary in the room. A teacher comes around and pushes upon
the desk in an effort to start it into a state of motion. The desk does not budge
. The desk remains at rest
because ______.
a.
there is a force of static friction opposing its motion
b.
there is a force of kinetic or sliding friction opposing its motion
c.
there is a force of rolling friction opposing its motion
d.
there are small dust mites at the desk's feet that push back on the desk to keep it at rest
800 N, left
0 N
1.0 m/s2, left
0 m/s2
I
FBD: Fx = 0 N, Fy = 686 N, ax = 0 m/s^2.
BD: Fx = 30 N, Fy = 196 N, ax = 1.0 m/s^2
Fx = 800 N, ax = -1 m/s^2, ay = 0 N
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Newton's Laws Name: Page 23 2.
A classroom desk supported by long legs is stationary in the room. A teacher comes around and pushes upon
the desk in an effort to start it into a state of motion. The desk is finally accelerated from rest and then
moves at a constant speed of 0.5 m/s. The desk maintains this constant speed because ______.
a.
there is a force of static friction balancing the teacher's forward push
b.
there is a force of kinetic or sliding friction balancing the teacher's forward push
c.
there is a force of rolling friction balancing the teacher's forward push
d.
the teacher must have stopped pushing
3.
The symbol μ
stands for the _____
a.
coefficient of friction b. force of friction
c.
normal force
4.
The units on μ
are _____
a.
Newton
b.
kg
c.
m/s/s
d.
... nonsense! There are no units on μ
.
5.
Use the friction equation and F
net
= m•a to fill in the blanks in the following situations.
Air Resistance and Terminal Velocity 0.83
0.51
0.825
28.5
right
Ian Torregrosa
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Newton's Laws Page 24 1.
When falling under the influence of air resistance and dropped
from the same height, which will fall to the ground at a faster rate?
a.
a mouse
b. an elephant c. the same
2.
Which of the following variables will have a direct effect upon the
amount of air resistance experienced by an object?
(That is, for which of these quantities will an increase lead to a
resulting increase in the air resistance force?)
a.
speed
b.
air density
c.
cross-sectional area
3.
Consider the dragster's motion below. Speedometer readings and the forward propulsion force (Fapp) are
shown. The top (or terminal) speed is 120 mph. Draw Fair force arrows on each diagram to illustrate how
the amount of air resistance changes during the course of its motion.
4.
Draw Fair force arrows to show how the force of air resistance changes on the falling skydiver. At A
, the
diver has just jumped; and at E
, the diver has just reached terminal velocity.
5.
Fill in the blanks in the following paragraph.
As an object moves faster and faster, the amount of air resistance __
increases
_____________ (increases,
decreases) until a state of terminal velocity is reached. Once terminal velocity is reached, the force of air
resistance is ____
equal to
____________ (greater than, less than, equal to) the force of gravity. Hence, the object
will __
stop it's acceleration
_________________________________ (continue to accelerate, stop its motion, stop its
acceleration, move back up to its starting position).
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Newton's Laws Name: Page 25 Skydiving A 90-kg (approx.) skydiver jumps out of a helicopter at 6000 feet above the ground. As he descends, the force of air resistance acting upon him continually changes. The free-body diagrams below represent the strength and direction of the two forces acting upon the skydiver at six positions during his fall. For each diagram, apply Newton’s second law (F
net
= m•a) to determine the acceleration value. 1.
At which two altitudes has the skydiver reached terminal velocity?
2.
At which altitude(s) is the skydiver in the state of speeding up?
3.
At which altitude(s) is the skydiver in the state of slowing down?
Ian Torregrosa
10, down
7.77, down
0
2.22, up
6.66, up
0
4500 ft, 1500 ft
6000 ft, 5500 ft
3000 ft, 2900 ft
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Newton's Laws Page 26 4.
At 2900 feet, the skydiver is ___________. Choose two.
a.
moving upward
b. moving downward c. speeding up
d. slowing down
5.
Explain why air resistance increases from 6000 feet to 4500 feet.
6.
Explain why air resistance decreases from 3000 feet to 1500 feet.
The Elephant and the Feather Without Air Resistance Suppose that an elephant and a feather are dropped off a very tall building from the same height at the same time. Suppose also that air resistance could be eliminated such that neither the elephant nor the feather would experience any air drag during the course of their fall. Which object - the elephant or the feather - will hit the ground first? Many people are surprised by the fact that in the absence of air resistance, the elephant and the feather strike the ground at the same time. Why is this so? Test your understanding by identifying the following statements as being either True (
T
) or False (
F
). 1.
The elephant and the feather each have the same force of gravity.
2.
The elephant has more mass, yet they both experience the same force of gravity.
3.
The elephant experiences a greater force of gravity, yet both the elephant and the feather have the same
mass.
4.
On earth, all objects (whether an elephant or a feather) have the same force of gravity.
5.
The elephant weighs more than the feather, yet they each have the same mass.
6.
The elephant clearly has more mass than the feather, yet they each weigh the same.
7.
The elephant clearly has more mass than the feather, yet the amount of gravity (force) is the same for each.
8.
The elephant has the greater acceleration, yet the amount of gravity is the same for each.
With Air Resistance Now consider the realistic situation that both feather and elephant encounter air resistance. Which object - the elephant or the feather - will hit the ground first? Most people are not surprised by the fact that the elephant strikes the ground before the feather. But why does the elephant fall faster? Test your understanding by identifying the following statements as being either True (
T
) or False (
F
). 1.
The elephant encounters a smaller force of air resistance and therefore falls faster.
As you increase, you hit more air particles per unit of time
As the parachute opens surface are up, thus up F air. The skydiver slows down as a result F air > Fg. As skydiver slows F air down until new terminal reached.
False
False
False
False
False
False
False
False
False
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Newton's Laws Name: Page 27 2.
The elephant has the greater acceleration of gravity and therefore falls faster.
3.
Both elephant and feather have the same force of gravity, yet the acceleration of gravity is greatest for the
elephant.
4.
Both elephant and feather have the same force of gravity, yet the feather experiences a greater air
resistance.
5.
Each object experiences the same amount of air resistance, yet the elephant experiences the greatest force
of gravity.
6.
Each object experiences the same amount of air resistance, yet the feather experiences the greatest force of
gravity.
7.
The feather weighs more, and therefore will not accelerate as rapidly as the elephant.
8.
Both elephant and feather weigh the same amount, yet the greater mass of the feather leads to a smaller
acceleration.
9.
The elephant experiences less air resistance and reaches a larger terminal velocity.
10.
The feather experiences more air resistance and thus reaches a smaller terminal velocity.
11.
The elephant and the feather encounter the same amount of air resistance, yet the elephant has a greater
terminal velocity.
Newton's Third Law A force is a push or pull resulting from an interaction between two objects. Whenever there is a force, there are two objects involved - with both objects pushing (or pulling) on each other in opposite directions. While the direction of the pushes (or pulls) is opposite, the strength or magnitude is equal. This is sometimes stated as Newton's Third Law of motion: for every action, there is an equal and opposite reaction
. A force is a push or a pull and it always results from an interaction between two objects. These forces always come in pairs. Ian Torregrosa
Fals
e
Fals
e
False
False
False
False
Fals
e
False
False
False
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Newton's Laws Page 28 1.
For each stated action force
, identify the reaction force
.
Bat hits ball. Man pushes car. Bus hits bug. 2.
Identify by words the action-reaction force pairs in each of the following diagrams.
Ball hits bat
Car pushes man
Bug hits bus
Athlete pushes ball
Ball pushes athlete
Foot pushes floor
Floor pushes foot
Foot kicks ball
Ball kicks foot
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Newton's Laws Name: Page 29 3.
TRUE
or FALSE
:
As you sit in your seat in the physics classroom, the Earth pulls down upon your body with a gravitational force; the reaction force is the chair pushing upwards on your body with an equal magnitude. If False, correct the answer. 4.
Shirley Bored sits in her seat in the English classroom. The Earth pulls
down on Shirley's body with a gravitational force of 600 N. Describe the
reaction force of the force of gravity acting upon Shirley.
5.
Use Newton's third law (law of action-reaction) and Newton's second law (law of acceleration: a = Fnet/m)
to complete the following statements by filling in the blanks.
a.
A bullet is loaded in a rifle and the trigger is pulled. The force experienced by the bullet is __
equal
to
__________
(less than, equal to, greater than) the force experienced by the rifle. The resulting
acceleration of the
bullet is ___
greater than
_________ (less than, equal to, greater than) the resulting
acceleration of the rifle.
b.
A bug crashes into a high-speed bus. The force experienced by the bug is __
equal to
___ (less than, equal
to, greater than) the force experienced by the bus. The resulting acceleration of the bug is
__
greater than
__________ (less than, equal to, greater than) the resulting acceleration of
the bus.
c.
A massive linebacker collides with a smaller halfback at midfield. The force experienced by the
linebacker is _
equal to
___________ (less than, equal to, greater than) the force experienced by the
halfback.
The resulting acceleration of the linebacker is __
less than
__________ (less than, equal to,
greater than) the
resulting acceleration of the halfback.
Ian Torregrosa
False - Earth pulls you, you pull Earth
Shirley pulls with a force of 600 N on the Earth
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Newton's Laws Page 30 d.
The 10-ball collides with the 14-ball on the billiards table (assume equal mass balls). The force
experienced by the 10-ball is _
equal to
___________ (less than, equal to, greater than) the force
experienced by
the 14-ball. The resulting acceleration of the 10-ball is __
equal to
__________ (less than,
equal to, greater than)
the resulting acceleration of the 14-ball.
Newton's Second Law Problem-Solving For the following problems, construct a free-body diagram and show your work clearly. 1.
A rightward force of 302 N is applied to a 28.6-kg crate to accelerate it across the floor. The coefficient of
friction between the crate and the floor is 0.750. Determine the acceleration of the crate.
2.
During a football workout, two linemen are pushing the coach on the sled. The combined mass of the sled
and the coach is 300 kg. The coefficient of friction between the sled and the grass is 0.800. The sled
accelerates at a rate of 0.580 m/s/s. Determine the force applied to the sled by the lineman.
3.
A 405-N rightward force is use to drag a large box across the floor with a constant velocity of 0.678 m/s. The
coefficient of friction between the box and the floor is 0.795. Determine the mass of the box.
4.
A 6.58 x 103 N upward tension force is exerted on a 521-kg downward-moving freight elevator. Determine
the acceleration of the elevator.
Fg = 5210 N
Fnet = 6580 N - 5210 N = 1370 N, UP
a = FNET/M = 1370 N, UP/521 kg = 2.63 m/s2, UP
The acceleration of the crate can be found using:
net force = mass x acceleration
acceleration = net force / mass
acceleration = 91.79 N / 28.6 kg
acceleration = 3.21 m/s2
F frict = 0.8 x (300 x 9.81)
F frict = 2354.4 N
F players - 2354.5 = 300 x 0.580
F players = 2528.4 N In balanced forces, the two individuals forces act in opposite direction. Conversely, in unbalanced forces,
the individual forces either act in same or opposite direction. A non-contact force is a force which acts on an object without coming physically in contact with it.
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Newton's Laws Name: Page 31 5.
A basketball star exerts a force of 3225 N (average value) upon the gym floor in order to accelerate his 76.5-
kg body upward. (a) Determine the acceleration of the player. (b) Determine the final speed of the player
if the force endures for a time of 0.150 seconds.
6.
At the end of the Giant Drop free fall ride, riders experience a large upward normal force to bring their falling
bodies to a stop. Determine the normal force value required to accelerate a 52.1-kg physics student with an
upward acceleration of 27.4 m/s/s.
7.
A hockey player accelerates a puck (m = 0.167 kg) from rest to a velocity of 50 m/s in 0.0121 sec. Determine
the acceleration of the puck and the force applied by the hockey stick to the puck. Neglect resistance forces.
8.
A falling skydiver is accelerating in the downward direction at 3.29 m/s/s. The mass of the skydiver (including
parachute gear) is 67.2 kg. Determine the air resistance force on the skydiver (and accompanying parachute).
9.
A 67.2-kg falling skydiver opens his parachute and instantly slows down at a rate of 7.2 m/s/s. Determine the
air resistance force on the skydiver (and accompanying parachute).
Ian Torregrosa
Fg= 765 N A) a = FNET/M = 2460 N, UP/76.5 kg = 32.16 m/s2, UP
Fnet = 2460 N, UP B) v = at = (32.16 m/s2)(0.150s) = 4.82 m/s, up
Fg= 521 N
Fnet = (52.1 kg) (27.4 m/s2) = 1427.54 N
FN= 1427.54 N + 521 N = 1948.54 N, UP
50m/s / 0.0121s = 4132.23 m/s2
FNET = Fapp = (0.167 kg)(4132.23 m/s2) = 690.08 N
Fg = 672 N
Fnet = (67.2 kg)(3.29 m/s2, 0) = 221.09 N
Fair = 672 N -221.09 N = 450.91 N
Fnet = (67.2 kg)(7.2 m/s2, up) = 483.84 N, up
Fair = 672 N + 483.84 N = 1155.84 N, UP
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