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1 year ago

14

On a cold winter day when the temperature is −20∘C, what amount of heat is needed to warm to body temperature (37 ∘C) the 0.50 L

of air exchanged with each breath? Assume that the specific heat of air is 1020 J/kg⋅K and that 1.0 L of air has mass 1.3×10−3kg.

1 answer:

vlabodo [156]1 year ago

4 0

Answer:

75.6J

Explanation:

Hi!

To solve this problem we must use the first law of thermodynamics that states that the heat required to heat the air is the difference between the energy levels of the air when it enters and when it leaves the body,

Given the above we have the following equation.

Q=(m)(h2)-(m)(h1)

where

m=mass=1.3×10−3kg.

h2= entalpy at 37C

h1= entalpy at -20C

Q=m(h2-h1)

remember that the enthalpy differences for the air can approximate the specific heat multiplied by the temperature difference

Q=mCp(T2-T1)

Cp= specific heat of air = 1020 J/kg⋅K

Q=(1.3×10−3)(1020)(37-(-20))=75.6J

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Suppose an electrical wire is replaced with one having every linear dimension doubled (i.e., the length and radius have twice th

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Answer:

The new resistance becomes half of the initial resistance.

Explanation:

The resistance of a wire is given by :

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New resistance of wire is given by :

$R'=\dfrac{\rho L'}{A'}$

$R'=\dfrac{\rho (2L)}{\pi (2r)^2}$

$R'=\dfrac{1}{2}\dfrac{\rho L}{A}$

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The new resistance becomes half of the initial resistance. Hence, this is the required solution.

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2 years ago

The lighting needs of a storage room are being met by six fluorescent light fixtures, each fixture containing four lamps rated a

Amanda [17]

Answer:

amount of energy = 4730.4 kWh/yr

amount of money = 520.34 per year

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Explanation:

given data

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to find out

the amount of energy and money that will be saved and simple payback period if the purchase price of the sensor is $32 and it takes 1 h to install it at a cost of $66

solution

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ΔE = 4730.4 kWh/yr

and

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1 year ago

(Double points) A machine receives electricity that enables it to deliver a total of 8,542 N of force for the completion of its

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Explanation:

Efficiency of a machine is the capability of a machine to convert input to output without waste.

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Efficiency = 7,023N/8,542N × 100%

Efficiency = 82.2%

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1 year ago

Paintball guns were originally developed to mark trees for logging. A forester aims his gun directly at a knothole in a tree tha

emmasim [6.3K]

Answer:

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Explanation:

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Using the equation of motion of the trajectory

The horizontal displacement of the paint ball is

$x=(u\cos\theta)t$

$t=\dfrac{x}{u\cos\theta}$

Using the equation of motion of the trajectory

The vertical displacement of the paint ball is

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Put the value into the formula

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2 years ago

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Answer:

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Outbound flight 7 hours 9 minutes

Return flight 6 hours 15 minutes

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1 year ago