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jekas [21]
2 years ago
10

A heat pump is to be used for heating a house in winter. The house is to be maintained at 70°F at all times. When the temperatur

e outdoors drops to 40°F, the heat losses from the house are estimated to be 75,000 Btu/h. Determine the minimum power [Btu/h] required to run this heat pump if heat is extracted from the outdoor air at 40°F.
Physics
1 answer:
Anna35 [415]2 years ago
3 0

Answer:

\dot{W_{H} } = 4244.48 Btu/h

Explanation:

Temperature of the house, T_{H} = 70^{0} F

Convert to rankine, T_{H} = 70^{0}+ 460 = 530 R

Heat is extracted at 40°F i.e T_{L} = 40^{0}F  = 40 + 460 = 500 R

Calculate the coefficient of performance of the heat pump, COP

COP = \frac{T_{H} }{T_{H} - T_{L}  } \\COP = \frac{530 }{530 - 500  }\\ COP = \frac{530}{30} \\COP = 17.67

The minimum power required to run the heat pump is given by the formula:

\dot{W_{H} } = \frac{\dot{Q_{H} }}{COP} \\...............(*)

Where the heat losses from the house, \dot{Q_{H} } = 75,000 Btu/h

Substituting these values into * above

\dot{W_{H} } = \frac{75000}{17.67} \\ \dot{W_{H} } = 4244.48 Btu/h

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Assoli18 [71]

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8 0
3 years ago
I know how the voltage increasing/not enough/stays the same and how long the battery lasts with series and parallel connections.
kirill [66]

Answer:

It comes out the positive side of the battery and goes in to the negative side of the battery

Explanation:

There are already electrons in wires in a circuit before you add the battery. By adding the battery, you're giving the electrons the energy it needs to move along the circuit.

In a series circuit, the circuit is one continuous loop so there is only one path for the electrons to go - out of the positive side of the battery and around the circuit then goes back into the negative side of the battery.

However, with a parallel circuit, there are two or more ways the electrons can go so they take the path of least resistance. The electrons still go out the positive side of a battery but along the circuit, the electrons will go through the path of least resistance ( I tend to think of it like a net with holes in it - the lower the resistance the bigger the holes for the electrons to go through so more can fit in a set amount of time ) but the electrons still go out of the positive side and in through the negative

3 0
2 years ago
The work done by an external force to move a -6.70 μc charge from point a to point b is 1.20×10−3 j .
ASHA 777 [7]

Answer:

108.7 V

Explanation:

Two forces are acting on the particle:

- The external force, whose work is W=1.20 \cdot 10^{-3}J

- The force of the electric field, whose work is equal to the change in electric potential energy of the charge: W_e=q\Delta V

where

q is the charge

\Delta V is the potential difference

The variation of kinetic energy of the charge is equal to the sum of the work done by the two forces:

K_f - K_i = W + W_e = W+q\Delta V

and since the charge starts from rest, K_i = 0, so the formula becomes

K_f = W+q\Delta V

In this problem, we have

W=1.20 \cdot 10^{-3}J is the work done by the external force

q=-6.70 \mu C=-6.7\cdot 10^{-6}C is the charge

K_f = 4.72\cdot 10^{-4}J is the final kinetic energy

Solving the formula for \Delta V, we find

\Delta V=\frac{K_f-W}{q}=\frac{4.72\cdot 10^{-4}J-1.2\cdot 10^{-3} J}{-6.7\cdot 10^{-6}C}=108.7 V

4 0
2 years ago
Read 2 more answers
A force of 5N compresses a spring by 4cm. Find the force constant of the spring.​
marissa [1.9K]

Answer:

k = 1,250 N/m

Explanation:

Use the formula F=kx, with F=5N and x=0.04m

Then the spring constant (k) is 5/0.04

6 0
3 years ago
A lab technician needs to clean medical instruments that have been exposed to bacteria. Which electromagnetic wave
sveta [45]

Answer:

Ultraviolet wave

Explanation:

Ultraviolet waves would be best used to sterilize a surface expose to bacteria because it will completely destroy them.

Most medical equipment are usually sanitized by using this rays because the DNA of most bacteria can be innervated upon exposure to these ray.

Ultraviolet rays are energetic and more powerful than the normal visible light and subsequent long wavelength radiations.

Generally, ultraviolet rays is a very harmful electromagnetic radiation.  

3 0
2 years ago
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