10 work, energy, and machines - weebly20. work and power does the work required to lift a book to a...
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10 Work, Energy, and Machines BIGIDEAWrite the Big Idea for this chapter.
Use the “What I Know” column to list the things you know about the Big Idea. Then list the questions you have about the Big Idea in the “What I Want to Find Out” column. As you read the chapter, fill in the “What I Learned” column.
KWhat I Know
WWhat I Want to Find Out
LWhat I Learned
Science Notebook • Work, Energy, and Machines149
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REVIEW VOCABULARY
law of conservation of
momentum
MAIN IDEAWrite the Main Idea for this section.
Recall and write the definition of the Review Vocabulary term.
law of conservation of momentum
Use your book to define each term.
work
joule
energy
work-energy theorem
kinetic energy
translational kinetic energy
power
watt
10 Work, Energy, and Machines 1 Work and Energy
NEW VOCABULARY
work
joule
energy
work-energy theorem
kinetic energy
translational kinetic
energy
power
watt
Science Notebook • Work, Energy, and Machines150
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Complete the sentence.
When a force applied at an angle causes an object to move horizontally,
only the of the force does work.
GET IT? Determine the work you do when you exert a force of 3 N at an angle of 45° from the direction of motion for 1 m.
Draw a force diagram showing the force you exert (Fme) to the right on a box and the force your friend exerts (Ffriend) to the left on the box. As a result of these two forces, the box moves to the right. Also show the gravitational force and the normal force. Explain why some forces do no work on the box.
GET IT? Explain why you do positive work on the box and your friend does negative work on the box.
GET IT? Describe another scenario in which you do work on a system, and explain how much work is done on the system.
Student Edition, pp. 264–266
1 Work and Energy (continued)
Science Notebook • Work, Energy, and Machines151
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Summarize how you can use a force-displacement graph to determine the work done in each case.
• If the force is constant
• If the force increases linearly
TRY IT !
ProblemAn ice skater slides toward a sled sitting on the ice and hits against it. The skater exerts a 12.6-N force on the sled at an angle of 15.3° below the horizontal. The sled then moves 15.4 m forward. How much work did the skater do on the sled? Assume friction is negligible.
1. ANALYZE AND SKETCH THE PROBLEM
KNOWNS UNKNOWNS
F = d = = ?
θ =
What is the system?
What is the force that is doing work on the system?
2. SOLVE FOR THE UNKNOWN
Write the equation for work. Then insert the known quantities.
3. EVALUATE THE ANSWER
• Explain why your units for work are correct.
• Explain why the sign of the answer is correct.
Student Edition, pp. 267–269
Use with Example Problem 2.
Use this column for
scratch work and
sketches.
1 Work and Energy (continued)
Science Notebook • Work, Energy, and Machines152
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Give an example of a force that does work on a system. Then use the work-energy theorem to your example.
Write a sentence using the word energy with its science usage and a sentence using the word energy with its common usage.
Science usage
Common usage
Describe the relationship between each of the following pairs of quantities.
work and energy
power and energy
power and work
Student Edition, pp. 270–271
1 Work and Energy (continued)
Science Notebook • Work, Energy, and Machines153
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Write work, energy, or power beside each unit to identify the quantity that it measures. Some quantities are measured by more than one unit. Some units are used for more than one quantity.
Units Quantities
kg�m2/s2
W
J/s
J
TRY IT !
ProblemMoving ocean water exerts a force of 375 N on a boat, causing the boat to move a distance of 34.7 m in 8.34 s. What power does the boat produce in kW?
1. ANALYZE AND SKETCH THE PROBLEM
KNOWNS UNKNOWNS
d = = ?
t =
F =
2. SOLVE FOR THE UNKNOWN
Use the definition of power.
3. EVALUATE THE ANSWER
• Explain why your units for power are correct.
• Explain why the sign of the answer is correct.
Student Edition, pp. 270–272
Use with Example Problem 3.
Use this column for
scratch work and
sketches.
1 Work and Energy (continued)
Science Notebook • Work, Energy, and Machines154
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1 Work and Energy (continued)
Student Edition, p. 273 Identify the equation you would use to calculate power if you know the following quantities.
work and time force, distance, and time
time and change in energy force and velocity
SUMMARIZE
How does the MAINIDEA for this section relate to the chapter’s BIGIDEA?
REVIEW IT !
15. MAINIDEA If the work done on an object doubles its kinetic energy, does it double its speed? If not, by what ratio does it change the speed?
16. Work Murimi pushes a 20-kg mass 10 m across a floor with a horizontal force of 80 N. Calculate the amount of work done by Murimi on the mass.
17. Work Suppose you are pushing a stalled car. As the car gets going, you need less and less force to keep it going. For the first 15 m, your force decreases at a constant rate from 210.0 N to 40.0 N. How much work did you do on the car? Draw a force-displacement graph to represent the work done during this period.
Science Notebook • Work, Energy, and Machines155
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18. Work A mover loads a 185-kg refrigerator into a moving van by pushing it at a constant speed up a 10.0-m, friction-free ramp at an angle of inclination of 11°. How much work is done by the mover on the refrigerator?
19. Work A 0.180-kg ball falls 2.5-m. How much work does the force of gravity do on the ball?
20. Work and Power Does the work required to lift a book to a high shelf depend on how fast you raise it? Does the power required to lift the book depend on how fast you raise it? Explain.
21. Power An elevator lifts a total mass of 1.1×103 kg a distance of 40.0 m in 12.5 s. How much power does the elevator deliver?
22. Mass A forklift raises a box 1.2 m and does 7.0 kJ of work on it. What is the mass of the box?
23. Work You and a friend each carry identical boxes from the first floor of a building to a room located on the second floor, farther down the hall. You choose to carry the box first up the stairs, and then down the hall to the room. Your friend carries it down the hall on the first floor, then up a different stairwell to the second floor. How do the amounts of work done by the two of you on your boxes compare?
24. Critical Thinking Explain how to find the change in energy of a system if three agents exert forces on the system at once.
1 Work and Energy (continued)
Science Notebook • Work, Energy, and Machines156
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-Hill Education. Perm
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