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Many decisions are made on the basis of the payback period: the time it will take through savings to equal the capital cost of an investment. Acceptable payback times depend upon the business or philosophy one has. (For some industries, a payback period is as small as 2 years.) Suppose you wish to install the extra insulation in the preceding problem. If energy cost $ 1.00 per million joules and the insulation was $4.00 per square meter, then calculate the simple payback time. Take the average Δ T for the 120-day heating season to be 15.0 ° C .

We found in the preceding problem that P = 126 Δ T W · ° C as baseline energy use. So the total heat loss during this period is Q = ( 126 J/s · ° C ) ( 15.0 ° C ) ( 120 days ) ( 86.4 × 10 3 s/day ) = 1960 × 10 6 J . At the cost of $1/MJ, the cost is $1960. From an earlier problem, the savings is 12% or $235/y. We need 150 m 2 of insulation in the attic. At $ 4 / m 2 , this is a $500 cost. So the payback period is $ 600 / ( $ 235 / y ) = 2.6 years (excluding labor costs).

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Additional problems

In 1701, the Danish astronomer Ole Rømer proposed a temperature scale with two fixed points, freezing water at 7.5 degrees, and boiling water at 60.0 degrees. What is the boiling point of oxygen, 90.2 K, on the Rømer scale?

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What is the percent error of thinking the melting point of tungsten is 3695 ° C instead of the correct value of 3695 K?

7.39 %

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An engineer wants to design a structure in which the difference in length between a steel beam and an aluminum beam remains at 0.500 m regardless of temperature, for ordinary temperatures. What must the lengths of the beams be?

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How much stress is created in a steel beam if its temperature changes from –15 ° C to 40 ° C but it cannot expand? For steel, the Young’s modulus Y = 210 × 10 9 N/m 2 from Stress, Strain, and Elastic Modulus . (Ignore the change in area resulting from the expansion.)

F A = ( 210 × 10 9 Pa ) ( 12 × 10 −6 / ° C ) ( 40 ° C ( −15 ° C ) ) = 1.4 × 10 8 N/m 2 .

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A brass rod ( Y = 90 × 10 9 N/m 2 ) , with a diameter of 0.800 cm and a length of 1.20 m when the temperature is 25 ° C , is fixed at both ends. At what temperature is the force in it at 36,000 N?

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A mercury thermometer still in use for meteorology has a bulb with a volume of 0.780 cm 3 and a tube for the mercury to expand into of inside diameter 0.130 mm. (a) Neglecting the thermal expansion of the glass, what is the spacing between marks 1 ° C apart? (b) If the thermometer is made of ordinary glass (not a good idea), what is the spacing?

a. 1.06 cm; b. 1.11 cm

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Even when shut down after a period of normal use, a large commercial nuclear reactor transfers thermal energy at the rate of 150 MW by the radioactive decay of fission products. This heat transfer causes a rapid increase in temperature if the cooling system fails ( 1 watt = 1 joule/second or 1 W = 1 J/s and
1 MW = 1 megawatt ) . (a) Calculate the rate of temperature increase in degrees Celsius per second ( ° C/s ) if the mass of the reactor core is 1.60 × 10 5 kg and it has an average specific heat of 0.3349 kJ/kg · ° C . (b) How long would it take to obtain a temperature increase of 2000 ° C , which could cause some metals holding the radioactive materials to melt? (The initial rate of temperature increase would be greater than that calculated here because the heat transfer is concentrated in a smaller mass. Later, however, the temperature increase would slow down because the 500,000-kg steel containment vessel would also begin to heat up.)

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Questions & Answers

I'm interested in biological psychology and cognitive psychology
Tanya Reply
what does preconceived mean
sammie Reply
physiological Psychology
Nwosu Reply
How can I develope my cognitive domain
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why is communication effective
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Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
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Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
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Wekolamo
because it helps many people around the world to understand how to interact with other people and understand them well, for example at work (job).
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ARC
A child is a member of community not society elucidate ?
JESSY Reply
Isn't practices worldwide, be it psychology, be it science. isn't much just a false belief of control over something the mind cannot truly comprehend?
Simon Reply
compare and contrast skinner's perspective on personality development on freud
namakula Reply
Skinner skipped the whole unconscious phenomenon and rather emphasized on classical conditioning
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explain how nature and nurture affect the development and later the productivity of an individual.
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nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
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I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
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interpersonal relationships
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What would be the best educational aid(s) for gifted kids/savants?
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Practice Key Terms 9

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Source:  OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
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