1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
jekas [21]
3 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]3 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

You might be interested in
light of a wavelength 600 nm shines on a soap bubble film. For what soap film thickness will destructive interference occur
VashaNatasha [74]

Answer:

The minimum thickness of the soap bubble for destructive interference to occur is 225.56 nm.

Explanation:

Given;

wavelength of light, λ = 600 nm

The minimum thickness of the soap bubble for destructive interference to occur is given by;

t = \frac{\lambda/n}{2}\\\\t = \frac{\lambda}{2n}

where;

n is refractive index of soap film = 1.33

t = \frac{\lambda}{2n} \\\\t = \frac{600*10^{-9}}{2(1.33)}\\\\t = 2.2556 *10^{-7} \ m\\\\t =  225.56 *10^{-9} \ m\\\\t = 225.56 \ nm

Therefore, the minimum thickness of the soap bubble for destructive interference to occur is 225.56 nm.

4 0
3 years ago
Describe how the number of photoelectrons emitted from a metal plate in the photoelectric effect would change if the following o
andrew-mc [135]

Answer:

a) True. The number of photoelectrons is proportional to the amount (intensity) of the incident beam. From the expression above we see that threshold frequency cannot emit electrons.

b)   λ = c / f

Therefore, as the wavelength increases, the frequency decreases and therefore the energy of the photoelectrons emitted,

c)  threshold energy

        h f =Ф

Explanation:

It's photoelectric effect was fully explained by Einstein by the expression

       Knox = h f - fi

Where K is the kinetic energy of the photoelectrons, f the frequency of the incident radiation and fi the work function of the metal

a) True. The number of photoelectrons is proportional to the amount (intensity) of the incident beam. From the expression above we see that threshold frequency cannot emit electrons.

b) wavelength is related to frequency

         λ = c / f

Therefore, as the wavelength increases, the frequency decreases and therefore the energy of the photoelectrons emitted, so there is a wavelength from which electrons cannot be removed from the metal.

c) As the work increases, more frequency radiation is needed to remove the electrons, because there is a threshold energy

        h f =Ф

7 0
3 years ago
What would be the answer for this and how?
Veronika [31]

Answer:

B. 6 cm

Explanation:

First, we calculate the spring constant of a single spring:

k = \frac{F}{\Delta x}\\

where,

k = spring constant of single spring = ?

F = Force Applied = 10 N

Δx = extension = 4 cm = 0.04 m

Therefore,

k = \frac{10\ N}{0.04\ m}\\k =  250\ N/m\\

Now, the equivalent resistance of two springs connected in parallel, as shown in the diagram, will be:

k_{eq} = k + k\\k_{eq} = 2k = 2(250\ N/m)\\k_{eq} = 500\ N/m\\

For a load of 30 N, applying Hooke's Law:

\Delta x = \frac{F}{k_{eq}}\\\\\Delta x = \frac{30\ N}{500\ N/m}\\\\\Delta x = 0.06\ m = 6\ cm\\

Hence, the correct option is:

<u>B. 6 cm</u>

7 0
3 years ago
What is the period of a 4.12 m long pendulum?
lisov135 [29]
Using the equation for period length, you get an answer of about 4.1 seconds.
8 0
3 years ago
The total resistance of resistors in parallel is always _________ the sum of the resistors.
docker41 [41]
A. less than

In fact, the resistance will be less than that of the lowest resistance resistor.
7 0
3 years ago
Read 2 more answers
Other questions:
  • Choose the best description of a magnetic field line
    9·2 answers
  • A wood block is sliding up a wood ramp. if the ramp is very steep, the block will reverse direction at its highest point and sli
    14·1 answer
  • Motion is defined by how fast an object is moving? True False
    6·2 answers
  • Find the color of light whose photon has 4.75x10^-19 J of energy
    10·1 answer
  • (a) Find the speed of waves on a violin string of mass 717 mg and length 24.3 cm if the fundamental frequency is 980 Hz. (b) Wha
    11·1 answer
  • Sound travels through air at 343 m/s at 20 °C. A bat emits an ultrasonic squeak and hears the echo 0.05 second later . How far a
    7·1 answer
  • A Ferris Wheel, starting from rest, undergoes a constant angular acceleration of 0.033 rad/s2 to get to its final operating angu
    12·1 answer
  • . A 6 ohm resistor is connected to a 15 volt battery.
    11·1 answer
  • a student taps the side of a stainless steel can containing water, making some sound waves travel from the stainless steel to th
    8·1 answer
  • Calculate the frequency of the wave shown below.
    13·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!