Notes

Question 1
(1 points)

(#695018) {Tension}



Which of the following statements is false about tension in a rope?

Select the correct answer
Tension in a rope is directed in the direction along the length of the rope.
The tension produced by a rope is a fixed force that depends on the length of the rope.
Your Answer
The SI unit of tension is Newtons.
Tension is a pulling force associated with a flexible connector.
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Question 2
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(#829435) {Tension/Equilibrium}



At the dance club, Chez Physique, the main elevator is decorated with a disco ball that hangs from the elevator's ceiling by a thin flexible wire.



Part a
(1 points)
Calculate the tension in the wire supporting the
7
.
4
1

k
g
7.41 kg disco ball when the elevator is sitting stationary on the 5th floor of a 10-story building.

Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8
72.6
N
Your Answer
Your actual answer was 72.62 which differs from the answer above by a small rounding error or significant figures. Check with your instructor how this will be graded in a testing situation.
Saved
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Part b
(1 points)
Calculate the tension in the wire supporting the
7
.
4
1

k
g
7.41 kg disco ball when the elevator is accelerating upwards with an acceleration of
�
=
+
1
.
5
4

m
/
s
2
a=+1.54 m/s
​2
​​

Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8
84
N
Your Answer
Your actual answer was 84.029 which differs from the answer above by a small rounding error or significant figures. Check with your instructor how this will be graded in a testing situation.
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Part c
(1 points)
Calculate the tension in the wire supporting the
7
.
4
1

k
g
7.41 kg disco ball when the elevator is accelerating downwards with an acceleration of
�
=
−
1
.
8
7

m
/
s
2
a=−1.87 m/s
​2
​​

Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8
58.8
N
Your Answer
Your actual answer was 58 which differs from the answer above by a small rounding error or significant figures. Check with your instructor how this will be graded in a testing situation.
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Question 3
(1 points)

(#299768) {Tension, Equilbrium}



A bird has a mass of 26 g and perches in the middle of a stretched telephone line. Determine the tension when
�
=
5
.
0
∘
θ=5.0
​∘
​​ . Assume that each half of the line is straight.

Image size: SMLMax



Select the correct answer
1.9 N
1.5 N
7.0 N
4.3 N
3.0 N
No answer submitted
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Question 4
(1 points)

(#665806){Tension, Equilibrium}



Two teams of nine members each engage in a tug of war. Each of the first team’s members has an average mass of 68 kg and exerts an average force of 1350 N horizontally. Each of the second team’s members has an average mass of 73 kg and exerts an average force of 1365 N horizontally. What is the tension in the section of rope between the teams?

Select the correct answer
1365 N
12,200 N
9000 N
135 N
1,100 N
No answer submitted
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Question 5
(1 points)

(#944842) {Inclined Planes}



A mass,
�
1
=
m
​1
​​ =8.15-kg mass is placed on a frictionless ramp which is inclined at 44.5
∘
​∘
​​ above the horizontal. It is connected to a second mass,
�
2
m
​2
​​ , by a strong rope which is run over a pulley at the apex of the ramp so that the second mass is suspended in the air next to the ramp, as shown in the figure. Calculate the mass,
�
2
m
​2
​​ necessary so that the mass,
�
1
m
​1
​​ accelerates up the incline at 1.63
�
/
�
2
m/s
​2
​​ .



Image size: SMLMax



Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
�
�
kg
No answer submitted
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Question 6
(1 points)

(#748724) {Spring Force}



Consider a mass on a spring. The mass is originally displaced a distance
�
x from its equilibrium condition and it experiences a restoring force due to the string,
�
�
F
​s
​​ . What is the new value,
�
�
′
F
​s
​′
​​ , of the spring's restoring force on the mass if the displacement is doubled to
2
�
2x?

Select the correct answer
�
�
′
=
4
�
�
F
​s
​′
​​ =4F
​s
​​
�
�
′
=
�
�
4
F
​s
​′
​​ =
​4
​
​F
​s
​​
​​
�
�
′
=
2
�
�
F
​s
​′
​​ =2F
​s
​​
Your Answer
�
�
′
=
�
�
F
​s
​′
​​ =F
​s
​​
�
�
′
=
�
�
2
F
​s
​′
​​ =
​2
​
​F
​s
​​
​​
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Question 7
(1 points)

(#352112) {Centripetal Force}



When an object experiences uniform circular motion, what is the direction of the net force?

Select the correct answer
Toward the center of the circular path
Your Answer
In the same direction as the motion
In the opposite direction of the motion
Away from the center of the circular path
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Question 8
(1 points)

(#027013) {Centripetal Force}



Nancy is running around a circular track encircling the reservoir where she grew up in Boston. As she's running, which of the following is true?

Select the correct answer
Her shoes need to exert a small, radially outward force on the ground to keep her body moving along the circular track.
Her shoes do not need to exert any force in the radial direction to keep her moving around the circle.
Her shoes need to exert a small, radially inward force on the ground to keep her body moving along the circular track.
Your Answer
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LAST ATTEMPT!

Question 9
(1 points)

(#314243) {Centripetal Force}



Car A goes around a curve of radius
�
1
R
​1
​​ at a speed of
�
1
V
​1
​​ . A little further down the road, the same car goes around a second curve with a radius of
�
2
=
1
2
�
1
R
​2
​​ =
​2
​
​1
​​ R
​1
​​ at a speed of
�
2
=
1
2
�
1
V
​2
​​ =
​2
​
​1
​​ V
​1
​​ (i.e., the second curve is half the radius of the first, and driven at half the speed as the first). What is the centripetal force on the car as it navigates the second curve compared to when it navigates the first. (i.e., what is the ratio :
�
�
,
2
�
�
,
1
)
​F
​c,1
​​
​
​F
​c,2
​​
​​ )?



Select the correct answer
Twice as big
A fourth as big
The same
Half as big
Four times as big
No answer submitted
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Question 10
(1 points)

(#325084) {Centripetal Force}



What size force is needed to keep a car of mass 1000kg moving around a circular track with radius 100m when the car is traveling at a constant speed of 24.3 m/s?

Give your answer in units of kilonewtons.

Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
kN
No answer submitted
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Question 11
(1 points)
PLEASE IGNORE THIS PROBLEM FOR NOW.

THIS PROBLEM IS "PREMATURE". IN PREVIOUS QUARTERS, WE TAUGHT ROTATIONAL MOTION (INCLUDING CENTRIPETAL FORCE) ONLY AFTER WE HAD DONE ENERGY AND MOMENTUM. AND ACTUALLY, ALTHOUGH IT INVOLVES CIRCULAR MOTION, IT CAN BE SOLVED PURELY WITH ENERGY AND MOMENTUM CONSIDERATIONS (NO CENTRIPETAL CALCULATIONS NECESSARY).




(#448708) {Centripetal Force}



A bullet of mass
�
=
1
2

g
m=12 g and moving horizontally with speed
�
v strikes a pendulum bob of mass
�
=
1
.
4
4
M=1.44
�
�
kg and becomes embedded in the bob. The bob is initially at rest, and is suspended by a stiff rod of length
�
=
0
.
8
9
8
L=0.898
�
m and negligible mass. The bob is free to rotate in the vertical direction about its pivot point at end of the rod opposite the end attahed to the bob. What is the minimum value of
�
v which causes the bob to execute a complete vertical circle?



Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
�
/
�
m/s
No answer submitted
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Question 12
(1 points)

(#743762) {Friction / Normal Force}



A book is pushed horizontally against a wall as shown in the figure. What are the forces that are exerted on the book and in what direction?

Image size: SMLMax



Select the correct answer
Normal force to the left, gravitational force downwards, force applied by the person pushing the book to the right, and force of friction upwards
Normal force to the right, gravitational force downwards, force applied by the person pushing the book to the right, and force of friction upwards
Normal force to the left, gravitational force downwards, force applied by the person pushing the book horizontally towards the left, and force of friction downwards
Normal force to the left, gravitational force upwards, force applied by the person pushing the book to the right, and force of friction downwards
Normal force to the right, gravitational force upwards, force applied by the person pushing the book to the left, and force of friction downwards
No answer submitted
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Question 13
(1 points)

(#244131) {Friction}



Consider a wood crate sitting stationary on a horizontal concrete floor so that the coefficient of static friction is 0.60. A person applies a constant horizontal force to the box, but the box remains stationary. Which of the following must be true in this situation?

Select the correct answer
The horizontal force must be equal to 0.6 times the weight of the crate.
The horizontal force must be less than the 0.6 times the weight of the crate.
The force due to friction must be zero
The force due to friction must be greater than the weight of the crate.
No answer submitted
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Question 14
(1 points)

(#194117) {Friction}



A burglar attempts to drag a 109 kg metal safe across a polished wood floor Assume that the coefficient of static friction is 0.4, the coefficient of kinetic friction is 0.3, and that the burglar can apply a pushing force of 509 N on the metal safe. What is the acceleration of the metal safe across floor?





Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m
/
s
2
m/s
​2
​​
No answer submitted
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Question 15
(1 points)

(#701238) {Multi-concept}




A cyclist is riding his bicycle down a hill at a speed of 15.0 m/s when he suddenly sees a car parked in the bicycle lane. He hits his brakes quickly, causing both of his tires to immediately "lock up" - which means that the wheels stop turning and the rubber of the tires start sliding against the asphalt, leaving a skid mark on the road. The length of the skid mark is 17.9 meters leads right up to the back of the parked car. The angle of the hill is 12.0
∘
​∘
​​ below the horizontal and the coefficient of kinetic friction between the road and the tires is 0.650. Determine the speed at which the cyclist hits the parked car.





Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m/s
No answer submitted
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Question 16
(1 points)

(#261083) {Drag}



A baseball thrown across an open field experiences a drag force that is best described in which of the two following regimes?



Select the correct answer
Quadratic Drag :
�
�
=
1
2
�
�
�
�
2
F
​D
​​ =
​2
​
​1
​​ CρAv
​2
​​
Linear Drag (Stokes' Law) :
�
=
−
6
�
�
�
�
F=−6πrηv
No answer submitted
0 of 1 checks used
LAST ATTEMPT!

Question 17
(1 points)

(#261447) {Drag}



The term "Marine snow" describe the slow shower of decaying organic materials from the upper layers of the ocean to the deeper layers. Organic aggregates on the order of a few millimeters in size can drift doward at a rate of 1-50 meters per day. The drag forces involved in this process would best be described in which of the two following regimes?

Select the correct answer
Quadratic Drag :
�
�
=
1
2
�
�
�
�
2
F
​D
​​ =
​2
​
​1
​​ CρAv
​2
​​
Linear Drag (Stokes' Law) :
�
=
−
6
�
�
�
�
F=−6πrηv
No answer submitted
0 of 1 checks used
LAST ATTEMPT!

Question 18
(1 points)

(#294621) {Drag}



Consider a car with an effective cross-sectional area of
2
.
5

m
2
2.5 m
​2
​​ , and a drag coefficient of
0
.
2
5
0.25. The car is moving at a speed of
2
9
.
7

m
/
s
29.7 m/s through air with a density of
1
.
2

k
g
/
m
3
1.2 kg/m
​3
​​ . Calculate the drag force on the car due to air resistance.



Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
N
No answer submitted
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Question 19
(1 points)

(#649184) {Drag}



A careful experiment on a playground determines that the drag force due to air resistance on a playground ball is
2
.
2
3

N
2.23 N when it is traveling through the air at a speed of
1
2
.
0

m
/
s
12.0 m/s. The diameter of the ball is
3
0
.
0

c
m
30.0 cm and the air has a density of
1
.
2
2

k
g
/
m
3
1.22 kg/m
​3
​​ . Calculate the drag coefficient of the playground ball.







Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
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Question 20
(1 points)

(#827101) {Drag}



In many science fiction movies (e.g., Star Wars' Mandalorian), people fly around with jet packs strapped to their back. Imagine that person jumps out of a plane with such a jet pack instead of a parachute, and that the thrust from the jet pack provides a constant upward force of 759

N
N. Assume that, including the jet pack, the person has a mass of 80.0

k
g
kg, and falls in a feet-first orientation so that they have a cross-section area of 0.200

m
2
m
​2
​​ and a drag coefficient of 0.700. Using 1.21

k
g
/
m
3
kg/m
​3
​​ as the density of the air, calculate the steady-state velocity at which this person will reach the ground.

Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m/s
No answer submitted
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Question 21
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(#879293) {Drag}



A 10-cm diameter metal ball falls through the air at its terminal velocity of
2
0
.
9

m
/
s
20.9 m/s.







Part a
(1 points)
Now imagine that we double the mass of the ball while keeping its diameter and its surface properties the same (i.e., same drag coefficient, C). One way we could do this would be to replace some portion of the inside of the ball with a higher density metal. What would the terminal velocity of this new ball be?





Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m/s
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Part b
(1 points)
Now imagine that we take the original ball and we double the diameter of the ball while keeping its mass and its surface properties the same (i.e., same drag coefficient, C). One way we could do this would be to make a larger version of the ball that is either partially hollow, or made of a less-dense material inside. What would the terminal velocity of this new ball be?





Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m/s
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Part c
(1 points)
Next, imagine that we take the original ball and we double the diameter of the ball but without changing the material or structure of the ball in any way. (Hint : with the same material and structure, the volume of the ball would increase as the diameter is increased ; as will the mass of the ball). What would the terminal velocity of this new ball be?





Please enter a numerical answer below. Accepted formats are numbers or "e" based scientific notation e.g. 0.23, -2, 1e6, 5.23e-8

Enter answer here
m/s
No answer submitted
0 of 5 checks used
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