Notes

Question 1
(1 points)

(746049) {Momentum}



If all objects in a system have non-zero momentum then the system has a non-zero momentum.



Select the correct answer
True
False
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LAST ATTEMPT!

Question 2
(1 points)

(806526) {Momentum}



Sidney, a football player with a mass of 103 kg and moving with a velocity of +9.27 m/s runs into a "wall" of opposing players and bounces backwards with a velocity of -1.19 m/s. What is the change in Sidney's momentum?



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
k
g
⋅
m
s
​s
​
​kg⋅m
​​
No answer submitted
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Question 3
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(259102) {Momentum}



Two crates of different masses sit on a frictionless ice rink. The same constant horizontal force is applied to each of the crates so the crates accelerate towards the east.



Part a
(1 points)
If the force is applied each crate for the same amount of time, which of the following is true?

Select the correct answer
The crates will end up with the same momenta.
The crates will end up with the same kinetic energies.
Both their momenta and their kinetic energies will be the same.
Neither their momenta nor their kinetic energies will be the same.
No answer submitted
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Part b
(1 points)
If the force is applied each crate over the same distance, which of the following is true?

Select the correct answer
The crates will end up with the same kinetic energies.
The crates will end up with the same momenta.
Both their momenta and their kinetic energies will be the same.
Neither their momenta nor their kinetic energies will be the same.
No answer submitted
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Question 4
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(433233) {Momentum}







Part a
(1 points)
Find the magnitude of the average net force required to stop a car with a mass of 1050 kg, initial speed is 40.0 km/h, and stopping distance 25.0 m.

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

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N
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Part b
(1 points)
Find the magnitude of the net force required to stop that same car in a duration of 2.5 seconds

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

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N
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Question 5
(1 points)

(697400) {Momentum}



When serving a tennis ball, a player hits the ball when its velocity is zero (at the highest point of a vertical toss). The racquet exerts a force of 634 N on the ball for 5.43 ms, giving it a final velocity of 46.7 m/s. Using these data, find the mass of the 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

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kg
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Question 6
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(574156) {Momentum}



In a head-on collision between two cars traveling at 20 m/s (44.7 mph), both cars are brought to a complete stop in 150 ms.



Part a
(1 points)
Calculate the restraining force required on a 70.9-kg passenger to remain firmly in their seat during such a head-on impact.



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

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Newtons
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Part b
(1 points)
The weight of an average 175-pound adult is 778 Newtons. Imagine if a person in the backseat of one of these cars chose not wear their seatbelt and instead attempted to use their arms to hold themselves against their seat back. To visualize the strength required to accomplish this, calculate the number of average adults this person would have to be able to hold up against gravity in order to accomplish this feat.



The restraining force in part (a) is equivalent to the combined weight of how many 175-pound adults?



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average adults
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Question 7
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(503513) {Impulse}



The force applied to an object varies with time as shown in the graph below.

Image size: SMLMax



Part a
(1 points)
Calculate the magnitude of the impulse delivered to the object.

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kg m/s
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Part b
(1 points)
If the object has a mass of 5.45 grams and is initially at rest, what is the final velocity of the object?

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m/s
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Question 8
(1 points)

(663943) {Impulse}



A cruise ship with a mass of
1
.
0
0
×
1
0
7

k
g
1.00×10
​7
​​ kg strikes a pier at a speed of 0.750 m/s. It comes to rest after traveling 6.00 m, damaging the ship, the pier, and the tugboat captain’s finances. Assuming that the ship experiences a constant deceleration during its collision with the pier, calculate the magnitude of the average force exerted on the pier using the concept of impulse. (Hint: First calculate the time it took to bring the ship to rest, assuming a constant force.)



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

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N
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Question 9
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(010342) {Pressure / Compressive Stress}



As a rough model of the impact of walking, consider that half of the mass of the entire body strikes the ground with a downward velocity of 1.0 m/s and comes to a full vertical stop over an impact duration of 20 ms.





Part a
(1 points)
Calculate the magnitude of the force associated with this single step for a person with a mass of 70.4 kg.











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

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N
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Part b
(1 points)
Calculate the stress (solid pressure) due to the force calculated in part (a) when applied across the 0.4 cm2 cross-sectional area of the typical Achilles tendon. For reference, the maximum rupture stress of tendons has been reported in the range of 100 - 150 MPa (Note; this number is given for reference only, it does not enter into this calculation). Give your answer in the units of MPa [Recall : 1 MPa = 106 Pa , and 1 Pa = 1 N/m2]









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

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MPa
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Question 10
(1 points)

(396079) {Conservation of Momentum}



Consider the situation of a ball bouncing off of a wall and having its momentum reversed. How much momentum is transferred into the wall in this perfectly elastic collision?

Select the correct answer
None, since the wall does not move.
An amount equal to the original momentum of the ball.
Half of the original momentum of the ball.
Twice the original momentum of the ball..
No answer submitted
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Question 11
(1 points)

(908963) {Inelastic Collisions}



Train cars are coupled together by being bumped into one another. Suppose two loaded train cars are moving toward one another, the first having a mass of
1
.
5
0
×
1
0
5

k
g
1.50×10
​5
​​ kg and a velocity of
(
0
.
3
0

m
s
)
�
^
(0.30
​s
​
​m
​​ )
​i
​^
​​ , and the second having a mass of
1
.
1
0
×
1
0
5

k
g
1.10×10
​5
​​ kg and a velocity of
(
−
0
.
1
2

m
s
)
�
^
(−0.12
​s
​
​m
​​ )
​i
​^
​​ . What is their final velocity?

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

m
s

�
^

​s
​
​m
​​
​i
​^
​​
No answer submitted
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Question 12
(1 points)

(971829) {Inelastic Collisions}



An object of mass 4 kg is moving to the right at a velocity of 6 m/s when it collides and sticks to a 6 kg object moving with a velocity of 5 m/s in the same direction. How much kinetic energy was lost in the collision?

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

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J
No answer submitted
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Question 13
(1 points)

(747807) {Multi-Concept}




A felt-covered beanbag is fired into a empty wooden crate that sits on a concrete floor and is open on one side. The beanbag is moving exactly horizontally when it strikes and sticks to the inside wall of the crate, which is lined with velcro. As a result of this impact, the crate slides backwards 0.801 meters along the concrete, which has a coefficient of kinetic friction of
�
�
=
0
.
5
3
3
μ
​k
​​ =0.533. The beanbag has a mass of 0.299 kg and the empty crate has a mass of 3.60 kg. Calculate the speed of the beanbag
�
v at the moment it strikes the crate. You may neglect the effect of air resistance.

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
m/s
No answer submitted
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Question 14
(1 points)
[You should definitely attempt this CHALLENGE question - but it will be counted as a BONUS QUESTION - it will not count against you if you miss it, but will add to your score if you get it correct!]




(#406972) {Multi-Concept}




Three plastic blocks are placed on a 1D frictionless rail and the bottom of the rail is glued to a large steel table. The first block (on the far left) has a mass of 24.0 kg and is launched rightward at 12.0 m/s. The second block has a mass of 11.4 kg and is stationary on the rail. The third block (on the far right) has a mass of 7.74 kg and is launched leftward at -2.00 m/s. Double-sided tape on the sides of the wood blocks cause them to stick together upon collision. After colliding, the combined blocks slide off of the frictionless rail and slide to a stop on the steel table. The coefficient of kinetic friction between the plastic and the steel table is 0.349. Neglect air resistance and calculate how many seconds the combined blocks slide along table surface (after leaving the rail) before coming to a stop.





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
seconds
No answer submitted
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Question 15
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(734740) {2D Inelastic Collisions}



A 20 kg child is sliding at 3 m/s across a frictionless frozen pond a -45 degrees relative to the x-axis, straight towards a dangerous hole in the ice. A physics professor is out for a stroll when he spots the child in peril and heroically launches herself across the ice at +30 degrees relative to the x-axis to intercept the child.

Image size: SMLMax



Part a
(1 points)
If the physics professor weighs 70.4 kg and launches herself across the ice with a velocity of 5 m/s. What is the magnitude of the velocity of the duo after the professor has grabbed the child?





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

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m/s
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Part b
(1 points)
At what angle (relative to the +x axis) with the duo be sliding after the rescue?









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

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Question 16
(1 points)

(1441479) {Elastic Collisions}



Two objects of masses 1 kg and 3 kg are held stationary on a frictionless surface with a compressed massless spring between them. When the blocks are released, the 1 kg object moves to the left with velocity 9 m/s. What is the velocity with which the 3kg object moves to the right.

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

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m/s
No answer submitted
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Question 17
(1 points)

(515108) {Elastic Collisions}



On a frictionless surface, a block of mass
�
1
=
2

k
g
m
​1
​​ =2 kg moves at a velocity of
�
1
�
=
+
6

m
/
s
v
​1i
​​ =+6 m/s (towards the right) headed towards another block of
�
2
=
1

k
g
m
​2
​​ =1 kg moving at a velocity of
�
2
�
=
−
3

m
/
s
v
​2i
​​ =−3 m/s (towards the left). The first block has an ideal massless spring mounted to its front side and so the collision between the blocks is perfectly elastic. Which set of final velocities is consistent with this collision?

Select the correct answer
�
1
�
=
+
3

m
/
s
v
​1f
​​ =+3 m/s ;
�
2
�
=
+
1

m
/
s
v
​2f
​​ =+1 m/s
�
1
�
=
−
9

m
/
s
v
​1f
​​ =−9 m/s ;
�
2
�
=
0

m
/
s
v
​2f
​​ =0 m/s
�
1
�
=
0

m
/
s
v
​1f
​​ =0 m/s ;
�
2
�
=
+
6

m
/
s
v
​2f
​​ =+6 m/s
�
1
�
=
+
3

m
/
s
v
​1f
​​ =+3 m/s ;
�
2
�
=
+
3

m
/
s
v
​2f
​​ =+3 m/s
�
1
�
=
0

m
/
s
v
​1f
​​ =0 m/s ;
�
2
�
=
+
9

m
/
s
v
​2f
​​ =+9 m/s
No answer submitted
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Question 18
(1 points)
[You should definitely attempt this CHALLENGE question - but it will be counted as a BONUS QUESTION - it will not count against you if you miss it, but will add to your score if you get it correct!]




(601239) {Multi-Concept}

/* {Elastic Collisions / Conservation of Energy / Kinetic Energy / Gravitational. Potential Energy}



A carnival game consists of a two masses on a curved frictionless track, as pictured below. The player pushes the larger object so that it strikes the stationary smaller object which then slides follows the curved track so that it rises vertically to a maximum height,
ℎ
�
�
�
h
​max
​​ . The masses are equipped with elastic bumpers so that the impact between them is an elastic collision. If the larger object has a mass ,
�
=
8
.
8
2

k
g
M=8.82 kg and the smaller object has a mass of
�
=
1
.
8
6

k
g
m=1.86 kg, then with what velocity,
�
0
v
​0
​​ should the player release the larger object so that the smaller object just reaches the target maximum height of
ℎ
�
�
�
=
3
.
0
�
h
​max
​​ =3.0m above the horizontal portion of the track?



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

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m/s
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Question 19
(1 points)

(538143) {Center of Mass}



A two-dimensional shape (grey region) is shown below, and is made of a material with uniform density. Each grid square in the diagram is d = 1.31 meters on a side. Calculate the x-coordinate of the shape's center of mass, assuming the bottom left corner sits at the origin (
�
=
0
x=0,
�
=
0
y=0) of our coordinate system.



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

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m
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Question 20
This question contains multiple parts. Make sure to read all the instructions and answer each part.

(332199) {Center of Mass}



A system consists of three blocks with masses on a frictionless surface as shown in the figure below.





Image size: SMLMax



Part a
(1 points)

The three blocks (from left to right in the figure) have masses of 3.04 kg, 0.696 kg and 7.96 kg. The leftmost block has a velocity of 3.58 m/s toward the right, the center block is stationary, and the rightmost block as a velocity of 2.56 m/s toward the left. Assuming movement toward the right is positive, what is the velocity of the center-of-mass of this system as pictured (prior to collision)?

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

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m/s
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Part b
(1 points)
Assume that all three block stick together upon collision. Once the collision (which may take part in two separate stages) is fully completed, what is the final velocity of the combined blocks?





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