CH 04 HW - Chapter 4 Physics Homework for Mastering PDF

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Chapter 4 Physics Homework for Mastering
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CH 04 HW Due: 3:00pm on Wednesday, September 25, 2019 You will receive no credit for items you complete after the assignment is due. Grading Policy

Adding and Subtracting Vectors Conceptual Question Six vectors (A to F) have the magnitudes and directions indicated in the figure.

Part A Which two vectors, when added, will have the largest (positive) x component?

Hint 1. Largest x component The two vectors with the largest x components will, when combined, give the resultant with the largest x component. Keep in mind that positive x components are larger than negative x components.

ANSWER:

C and E E and F A and F C and D B and D

Correct

Part B Which two vectors, when added, will have the largest (positive) y component?

Hint 1. Largest y component The two vectors with the largest y components will, when combined, give the resultant with the largest y component. Keep in mind that positive y components are larger than negative y components.

ANSWER:

C and D A and F E and F A and B E and D

Correct

Part C Which two vectors, when subtracted (i.e., when one vector is subtracted from the other), will have the largest magnitude?

Hint 1. Subtracting vectors To subtract two vectors, add a vector with the same magnitude but opposite direction of one of the vectors to the other vector.

ANSWER:

A and F A and E D and B C and D E and F

Correct

Problem 4.08 For each of the following situations, draw the forces exerted on the moving object and identify the other object causing each force.

Part A You pull a wagon along a level floor to the right using a rope oriented 45 above the horizontal. Draw a force diagram for the wagon. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

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Correct

Part B A bus moving on a horizontal road to the right slows in order to stop. Draw a force diagram for the bus. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

No elements selected

Select the elements from the list and add them to the canvas setting the appropriate attributes.

Correct

Part C You slide down an inclined at 30 water slide to the right. Draw your force diagram. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

No elements selected

Select the elements from the list and add them to the canvas setting the appropriate attributes.

Correct

Part D You lift your overnight bag into the overhead compartment on an airplane. Draw a force diagram for the bag. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

No elements selected

Select the elements from the list and add them to the canvas setting the appropriate attributes.

Correct

Part E A rope connects two boxes on a horizontal floor, and you pull horizontally on a second rope attached to the right side of the right box. Draw a force diagram for the right box. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

No elements selected

Select the elements from the list and add them to the canvas setting the appropriate attributes.

Correct

Part F A rope connects two boxes on a horizontal floor, and you pull horizontally on a second rope attached to the right side of the right box. Draw a force diagram for the left box. Draw the vectors starting at the black dot. The location and orientation of the vectors will be graded. The length of the vectors will not be graded. ANSWER:

No elements selected

Select the elements from the list and add them to the canvas setting the appropriate attributes.

Correct

Problem 4.28 A car has a mass of 1520

. While traveling at 29

, the driver applies the brakes to stop the car on a wet surface with a 0.40 coefficient of friction.

Part A How far does the car travel before stopping? Express your answer with the appropriate units. ANSWER: = 110

Correct

Part B If a different car with a mass 1.5 times greater is on the road traveling at the same speed and the coefficient of friction between the road and the tires is the same, what will its stopping distance be? ANSWER:

the stopping distance will be less than the stopping distance will be greater than the stopping distance will be the same as

Correct

Problem 4.46 - Enhanced - with Feedback The dogs of four-time Iditarod Trail Sled Dog Race champion Jeff King pull two 100horizontally.

sleds that are connected by a rope. The sleds move on an icy surface. The dogs exert a 240-

Part A Find the acceleration of the sleds. Express your answer with the appropriate units. ANSWER: = 1.2

Correct

Part B Find the force the rope between the sleds exerts on each sled. Express your answer with the appropriate units. ANSWER: = 120

Correct

Problem 4.34 A car with its wheels locked rests on a flatbed of a tow truck. The flatbed's angle with the horizontal is slowly increased. When the angle becomes 40 , the car starts to slide.

Part A Determine the coefficient of static friction between the flatbed and the car's tires. ANSWER: = 0.84

Correct

Problem 4.36 Bode Miller, 80-

downhill skier, descends a slope inclined at 17 .

Part A Determine his acceleration if the coefficient of friction is 0.10. Express your answer with the appropriate units. ANSWER: = 1.93

Correct

Part B How would this acceleration compare to that of a 160-

skier going down the same hill?

ANSWER:

The acceleration would be the same as

.

The acceleration would be greater than

.

The acceleration would be less than

.

Correct

Problem 4.58 A tennis ball is served from the back line of the court such that it leaves the racket 2.4

Part A Will the ball cross a 0.91- -high net 11.9 ANSWER:

no yes

in front of the server?

above the ground in a horizontal direction at a speed of 22.3

.

force on the rope attached to the front sled. The front rope pulls

Correct

Part B Determine the vertical position above the ground of the ball at a distance of 11.9

in front of the server.

Express your answer with the appropriate units. ANSWER: = 1.0

All attempts used; correct answer displayed

Part C Will the ball land in the service court, which is within 6.4

of the net on the other side of the net?

ANSWER:

yes no

Correct

Part D Determine the distance between the net (located at 11.9

in front of the server) and the position where the ball lands.

Express your answer with the appropriate units. ANSWER: = 3.7

Correct

± Arrow Hits Apple An arrow is shot at an angle of

above the horizontal. The arrow hits a tree a horizontal distance

away, at the same height above the ground as it was shot. Use

for the magnitude of the acceleration due to gravity.

Part A Find

, the time that the arrow spends in the air.

Answer numerically in seconds, to two significant figures.

Hint 1. Find the initial upward component of velocity in terms of D. Introduce the (unknown) variables

and

for the initial components of velocity. Then use kinematics to relate them and solve for

Express your answer symbolically in terms of

and

.

Hint 1. Find Find the horizontal component

of the initial velocity.

Express your answer symbolically in terms of

and given symbolic quantities.

ANSWER: =

Hint 2. Find What is the vertical component

of the initial velocity?

Express your answer symbolically in terms of

.

ANSWER: =

ANSWER: =

Hint 2. Find the time of flight in terms of the initial vertical component of velocity. From the change in the vertical component of velocity, you should be able to find Give your answer in terms of

in terms of

and .

and .

Hint 1. Find When applied to the y-component of velocity, in this problem the formula for

What is

, the vertical component of velocity when the arrow hits the tree?

Answer symbolically in terms of ANSWER: =

ANSWER:

only.

with constant acceleration

is

. What is the vertical component

of the initial velocity?

=

Hint 3. Put the algebra together to find

symbolically.

If you have an expression for the initial vertical velocity component in terms in terms of

and

, and another in terms of

and

, you should be able to eliminate this initial component to find an expression for

Express your answer symbolically in terms of given variables. ANSWER: =

ANSWER: = 6.7

Correct

Suppose someone drops an apple from a vertical distance of 6.0 meters, directly above the point where the arrow hits the tree.

Part B How long after the arrow was shot should the apple be dropped, in order for the arrow to pierce the apple as the arrow hits the tree? Express your answer numerically in seconds, to two significant figures.

Hint 1. When should the apple be dropped The apple should be dropped at the time equal to the total time it takes the arrow to reach the tree minus the time it takes the apple to fall 6.0 meters. Hint 2. Find the time it takes for the apple to fall 6.0 meters How long does it take an apple to fall 6.0 meters? Express your answer numerically in seconds, to two significant figures. ANSWER: = 1.1

ANSWER: = 5.6

Correct

Problem 4.72 A minivan of mass 1560

starts at rest and then accelerates at 1.8

.

Part A What external force accelerates the minivan? ANSWER:

friction force exerted by the surface on the minivan normal force exerted by the surface on the minivan gravitational force exerted by Earth on the minivan

Correct

Part B Air resistance and other opposing resistive forces are 300

. Determine the magnitude of the force that causes the minivan to accelerate in the forward direction.

Express your answer with the appropriate units. ANSWER: = 3.1

Correct

Problem 4.76 You abruptly push a 1.7-

Part A

book along a table and let go. The book comes to a stop after a short distance. shows the acceleration-versus-time graph of the book as recorded by a motion detector.

Estimate the maximum speed of the book. Select the correct answer. ANSWER:

37 18 2.3 0.1 0.2 1.2

Correct

Part B Estimate the clock reading when your hand stopped exerting the force on the book. Select the correct answer. ANSWER:

2.9 3.7 3.5 3.2

Correct

Direct Measurement Video: Falling Through the Air We will use a video to study the dynamics of objects falling through the air by analyzing the motion of three balls released from rest above the ground. Specifically, we will: 1. Examine the underlying principles behind the motion of falling objects. 2. Take measurements from the video of two of the balls' positions at various times to determine their accelerations. 3. Use Newton's Second Law to determine the impact of air resistance. In the video, you will analyze the motion of three falling objects and compute their accelerations using distance and time measurements. You will then compare these accelerations with the standard value of the acceleration due to gravity on Earth. Before you start taking the measurements using the video, let us make sure you understand the concepts and the calculations involved. A series of questions will guide you along the way.

Part A If an object is in free fall, which of the following statements must be true? Mark all the correct statements among those provided below.

Hint 1. Definition of free fall An object is in free fall if the only force acting on it is the force of gravity. Hint 2. How force relates to velocity and acceleration The net force acting on an object fully defines its acceleration but not its velocity. Hint 3. Initial velocity and free fall Free fall is defined in terms of the applied force or, sometimes, in terms of the acceleration–but it has nothing to do with the initial velocity.

ANSWER: The initial velocity is zero. The object is moving vertically. The object is moving downward. The only force acting on the object is the force of gravity. The only forces acting on the object are the forces of gravity and air resistance. The acceleration of the object is constant. The acceleration of the object is decreasing. The acceleration of the object is increasing.

All attempts used; correct answer displayed

Part B What are possible correct units for

in the SI system of units?

Mark all the correct statements among those provided below.

Hint 1. Newton's 2nd Law According to Newton's Second Law,

. What does this tell you about the relationship between the units of force, mass and acceleration?

Hint 2. May the units of force be with you… According to Newton's Second Law, the unit of acceleration is equivalent to the unit of force divided by the unit of mass.

ANSWER:

Correct

Part C What are possible correct units for weight in the SI system of units? Mark all the correct statements among those provided below.

Hint 1. Weight a minute…what a mass! Weight is often confused with mass. While these quantities are, indeed, related, they are not the same. Hint 2. May the product of mass and acceleration be with you! Weight is actually just a one-word nickname for the force of gravity acting on an object. Use the (units of) force!

ANSWER:

Correct Weight is actually just a one-word nickname for the force of gravity acting on an object. Many physics educators don't like the term since it can confuse in many students–but the term is very common, and you are likely to encounter it in you physics study materials including, probably, your textbook.

Part D What is the correct formula for of the weight

of an object? Assume that its mass is

, the magnitude of its acceleration is , and the local acceleration due to gravity is .

Select the best answer from the choices provided. ANSWER:

Correct The formula looks a lot like a case of Newton's Second Law–but, strictly speaking, it is not. Rather, it's a "recipe" for calculating the weight (or, more properly, the force of gravity) acting on an object. Note that in Newton's Second L is the actual acceleration of the object. However, in the formula , is a constant describing the strength of gravity at the location of the object, commonly (and somewhat misleadingly) known as "the acceleration due to gravity."Th value of depends on the planet the object is on and on the location of the object on that planet (altitude, etc.)–but it has nothing to do with the object's motion. The force of gravity acting on you does not change whether you sit, walk, run o jump up and down…unless, of course, you jump so hard, you never come down…but that's another story!However, combined with Newton's Second Law, formula leads to an important conclusion: if the force of gravity (a.k.a. weigh is the only force applied to an object, the object's acceleration will, indeed, be equal to , regardless of its mass or velocity. This motion is known as free fall. Let's see if the fall depicted in the video is, indeed, free.

Click play to watch the entire video (text description of video) that depicts three balls of very different masses released simultaneously and fall vertically, then answer the questions that follow.

Part E What statement best describes the relationship between the magnitudes of the accelerations of the balls? Select the best answer from the choices provided.

Hint 1. Which measuring tools to use None, really. Just watch the balls fall. Hint 2. What should be watched We recommend that you focus your attention on the bottom of each ball since they are all lined up at the moment of their release.

ANSWER:

The purple ball and the orange ball appear to have the same acceleration; the blue ball has a greater acceleration. All three balls appear to have the same acceleration The blue ball and the orange ball appear to have the same acceleration; the purple ball has a smaller acceleration. The purple ball and the orange ball appear to have the same acceleration; the blue ball has a smaller acceleration. The blue ball and the orange ball appear to have the same acceleration; the purple ball has a greater acceleration.

Correct Since the blue ball has a smaller acceleration, its fall does not appear to be "free", exactly. Let's explore the motion of the blue ball quantitatively, shall we

Part F Before we proceed with the calculations, let's make sure that the measuring tools are working for you. At what frame does the motion of the balls begin? Use the frame number displayed in the video itself as opposed to the one from the player bel Enter the integer number of the frame corresponding to the frame in which the three balls begin to move.

Hint 1. Where to find the answer Look at the frame counter that provides the frame number. Hint 2. Is it moving…or not? Look carefully at the bottoms of the balls and use your best judgment. At what point does the platform separate from the balls? You may want to toggle the frame advancement buttons back and forth to decide.

ANSWER: 130

Correct To provide consistency for further calculations, let's assume that all three balls begin to move at frame 130

Part G Now, let's consider the motion of the blue ball. What is the frame number that corresponds to the moment when the displacement of the blue ball is 0.10

?

Enter the integer number of the frame.

Hint 1. What to look for Consider the position of the bottom of the blue ball. Hint 2. Wait, where are the meters? The scale on the screen gives displacement in centimeters (

).

Hint 3. Identifying the correct frame To determine the frame number, just use your best judgment. It is understood that any measurement off a screen has some uncertainty to it.

ANSWER: 472

Correct It is difficult to be sure what frame, exactly, corresponds to any particular displacement–so, realistically, your results may differ from those of others. Meanwhile, in this particular pro...