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Guide | Help | My Options

Serway and Faughn - College Physics 7/e (Homework)

Chris Read

Mathematics and Sciences, section 1, Fall 2010

Instructor: Mr. Cengage

Current Score: 13/24

Due: Monday, September 20, 2010 11:00 PM EDT

About this Assignment

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Question

Points

1	2	3	4	5	6	7
3	1	0/4	1	6/7	0/6	2

Total

13/24

Description

College Physics by Serway and Faughn now has animations with conceptual questions and tutorial problems offering feedback and hints to guide student content mastery, as well as over 1600 end-of-chapter questions.

Students will see a detailed solution, in blue, using the algorithmically-generated values in the question, at the instructor's discretion--for example, after a particular submission or after the assignment due date has passed.

You can check out a sampling of this exciting development below. WebAssign is the most utilized homework system in physics. Designed by physicists for physicists, WebAssign, easy to use, reliable--a trusted companion to your teaching. Sign up for a Test Drive today!

Question 1 is a traditional end-of-chapter question, with conditional feedback for incorrect numerical answers. (For this demo, the solution is displayed immediately after the question has been submitted using the algorithmically-generated values.)

Question 2 is an end-of-chapter question enhanced by adding a link to an Active Figure. The solution is displayed after the question has been answered.

Question 3 and 4 show Active Figure questions which have been imported into WebAssign.

Question 5 is a new Active Example which helps guide students through the process needed to master a concept.

Question 6 is a Quick Quiz question with customized feedback added to the numerical portion.

Question 7 is a Math Review question from the math review appendix.

Click here for a list of all of the questions coded in WebAssign.

Instructions

This demo assignment allows many submissions and allows you to try another version of the same question for practice.

1. 3/3 points All Submissions Notes Question: SerCP7 4.P.015.soln.

Question part

Points

Submissions

1	2	3
1	1	1
10/50	8/50	6/50

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3/3

Find the tension in each cable supporting the 500 N cat burglar in Figure P4.15. Assume the angle

of the inclined cable is 34.0°.

inclined cable	Enter a number. 1 N
horizontal cable	Enter a number. 2 N
vertical cable	Enter a number. 3 N

Figure P4.15

A traditional end-of-chapter question, with conditional feedback for incorrect numerical answers. (For this demo, the solution is displayed immediately after the question has been submitted using the algorithmically-generated values.)

Note from WebAssign: All numerical end-of-chapter questions will give feedback to the student when an incorrect answer is submitted. Please see the algorithmically generated solution below.

2. 1/1 points All Submissions Notes Question: SerCP7 5.P.044.AF.

Question part

Points

Submissions

1
1
3/50

Total

1/1

A child slides without friction from a height h along a curved water slide (Fig. P5.44). She is launched from a height h/5 into the pool. Determine her maximum airborne height y in terms of h and

. (Use theta for

and h as appropriate.)

Click here for help with symbolic formatting.

Figure P5.44

Refer to the Active Figure Simulation to review the concepts this question addresses.

Hint: Active Figure 5.15

Note from WebAssign: The answer is any expression mathematically equal to

h/5 * (4*(sin(theta))^2 + 1)

Please see algorithmically generated solution below.

3. –/4 points Notes Question: SerCP7 4.AF.21.

Question part

Points

Submissions

1	2	3	4
0/1	0/1	0/1	0/1
0/50	0/50	0/50	0/50

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0/4

Active Figure 4.21 Acceleration Up and Down an Incline with Friction

The external forces exerted on a block lying on a rough incline are the gravitational force mg, the normal force n, and the force of friction f. For convenience, the gravitational force is here is resolved into a component along the incline and a component perpendicular to the incline.

Instructions: Turn friction on or off using the drag button and click start to project the block up the incline. You can use the back, pause and fwd buttons to stop the block's motion at any point and step through one frame at a time.

Exploration 1

For this Exploration, set the drag button to off. Reset the the block and start a sequence. Observe how the block rises to a highest point and then moves down the slope out of view. Reset the block and start another sequence, but this time use the pause, back and fwd button to freeze the block at its highest point. Record the time, distance and acceleration at this highest point. The acceleration graph in the upper right-hand corner of the screen shows that the acceleration is constant throughout the entire motion sequence. Why?

(a) From your results recorded above, find the following quantities.

The angle of the incline -- measured with respect to the horizontal.
°

From the block's given initial speed of 6.8 m/s up the incline, use the kinematic equation v² = v²₀ + 2ax to calculate the distance traveled up the incline. Does your calculated value equal the value recorded above?

Use another kinematic equation to calculate the time to reach the highest point. Does this value agree with the value recorded above?

Display in a New Window

Exploration 2

Click the drag button to introduce a kinetic frictional force on the block. Reset the block and run a full sequence. Notice in this case that the acceleration varies from a maximum value of 8.61 m/s² to a minimum value of 1.19 m/s².

To understand why the acceleration now changes, play the animation a few times, paying close attention to the free-body diagram. Use the pause button to play a few frames right around the highest point. Recall that friction always acts opposite to the direction of slide. So, while the block slides up the incline, the friction points down the incline -- and vice-versa.

To find the magnitude of the friction force, apply Newton's second law in a direction perpendicular to the incline.

F_y = -mg cos

= 0

f_k = µ_kn = µ_kmg cos

While the block is sliding up the incline (negative direction), Newton's second law applied in a direction parallel to the incline gives the following.

F_x = sin(

) + f_k = ma_up

However, when the block slides down the incline, Newton's second law becomes:

F_x = mg sin

- f_k = ma_down

(b) Use either of the last two equations to solve for the coefficient of kinetic friction. Double-check with the other equation.
µ_k =

Exercise 4.AF.21

Suppose that the coefficient of kinetic friction in the above animation is decreased to 0.288. Calculate the magnitude of acceleration up and down the incline.

4. 1/1 points All Submissions Notes Question: SerCP7 12.AF.02.

Question part

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Submissions

1
1
11/50

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1/1

Active Figure 12.2: Work Done on a Gas for Different PV Processes

In this animation, you can choose one of the three process simulations and see the simulation evolve in the corresponding PV diagram. Readouts are provided for the thermodynamic state variables P, V and T, and for the work done on the gas during the simulation. The area under the PV curve is shaded.

Instructions: Click one of the three sim buttons to see the process simulated by the piston and diagrammed in the PV graph.

Explore

Play each simulation, and pay attention to how the state variables change in each case. Compare the value indicated in the work readout to the shaded area under each PV-curve.

When you are ready, match the item on the left with the most appropriate item on the right. Do not match items that are identical in both columns.

isovolumetric followed by isobaric
simulation 1
simulation 2
isothermal
isobaric followed by isovolumetric

5. 6/7 points All Submissions Notes Question: SerCP7 4.AE.01.

Question part

Points

Submissions

1	2	3	4	5
0	0	5	0/1	1
1/50	1/50	1/50	1/50	5/50

Total

6/7

Example 4.1 Airboat

Goal Apply Newton's law in one dimension, together with the equations of kinematics.

Problem An airboat with mass 4.50

10² kg, including passengers, has an engine that produces a net horizontal force of 8.14

10² N, after accounting for forces of resistance.

(a) Find the acceleration of the airboat.

(b) Starting from rest, how long does it take the airboat to reach a speed of 16.0 m/s?

(c) After reaching this speed, the pilot turns off the engine and drifts to a stop over a distance of 50.0 meters. Find the resistance force, assuming it's constant.

Figure 4.4

Strategy In part (a), apply Newton's 2nd law to find the acceleration, and in part (b) use this acceleration in the one-dimensional kinematics equation for the velocity. When the engine is turned off in part (c), only the resistance forces act on the boat, so their net acceleration can be found from v² - v₀² = 2ax. Then Newton's second law gives the resistance force.

Solution

(a) Find the acceleration of the airboat.
Apply Newton's 2nd law to solve for the acceleration.	ma = F_net a = = a = Enter a number. 1 m/s²
(b) Find the time necessary to reach a speed of 16.0 m/s.
Apply the kinematics velocity equation:	v = at + v₀ = 16.0 m/s t = Enter a number. 2 s
(c) Find the resistance force after the engine is turned off.
Using kinematics, find the net acceleration due to resistance forces.	v² - v₀² = 2ax 0 - (16.0 m/s)² = 2a(50.0 m) a = Enter a number. 3 m/s²
Substitute the acceleration into Newton's second law, find the resistance force.	F_resist = ma = (4.50 10² kg)a F_resist = Enter a number. 4 N The answer you submitted has the wrong sign.
Remarks The negative answer for the acceleration in part (c) means that the airboat is slowing down. In this problem, the components of the vectors and were used, so they were written in italics without being bolded. It's important to bear in mind that and are vectors, not scalars.

Exercise 4.1

Hints: Getting Started | I'm Stuck

Suppose the pilot, starting again from rest, opens the throttle only partway. At a constant acceleration, the airboat then covers a distance of 63.7 meters in 10.5 seconds. Find the net force acting on the boat.

F =

Note from WebAssign
If a student makes one of several common mistakes on the Exercise portion above, they will get feedback specific to the mistake they made. If their answer is incorrect but does not meet one of these specific conditions, they will still get generic numerical feedback as to how far off they are, or if they appear to have made just a sign or order of magnitude error, etc.

Try some of these values to see what feedback you get!

Incorrect formula	Incorrect answer
md/t²	260.
(2md/t)²	2.98e+07
20md/t²	5.20e+03
md/(2t²)	130.
Correct formula	Correct answer
2md/t²	520.

6. 0/6 points All Submissions Notes Question: SerCP7 12.QQ.03.

Question part

Points

Submissions

1	2	3	4	5	6
0/1	0/1	0/1	0/1	0/1	0/1
1/50	1/50	1/50	1/50	1/50	1/50

Total

0/6

Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are as given below.

	T_h (K)	T_c (K)
Engine A	1,000	700
Engine B	800	500
Engine C	600	300

Rank the engines in order of theoretically possible efficiency, from highest to lowest.
Your answer is incorrect.

What is the efficiency of each engine?

Engine A	Enter a number. 4% Your answer differs by the correct answer by more than 10%.
Engine B	Enter a number. 5% Your answer differs by the correct answer by more than 10%.
Engine C	Enter a number. 6% Your answer differs by the correct answer by more than 10%.

7. 2/2 points All Submissions Notes Question: Math Review Question

Question part

Points

Submissions

1	2
1	1
2/50	3/50

Total

2/2

Note from WebAssign: Each Serway textbook includes a Math Review Appendix. One such question is below. For an assignment of Math Review questions click here.

Quadratic Equations

Solve the following quadratic equation.

x² + 7x - 8 = 0

x =

(smaller value)
x = Your answer is correct.

(larger value)

Refer to th.

Appendix A.3D

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