Consider a 30-cm-diameter hemispherical enclosure. The dome is maintained at 600 K, and heat is supplied from the dome at a rate of 65 W while the base surface with an emissivity of 0.55 is maintained at 400 K. Determine the emissivity of the dome.
Answer:
[tex]\epsilon_2=0.098[/tex]
Explanation:
Diameter [tex]d=30cm=0.3m[/tex]
Temperature [tex]T=600k[/tex]
Rate of supply [tex]r=65W[/tex]
Emissivity of base surface [tex]\in_b =0.55[/tex]
Temperature at base [tex]T_b=400k[/tex]
Generally the equation for Area of base surface is mathematically given by
[tex]A_b=\frac{\pi}{4}d^2[/tex]
[tex]A_b=\frac{\pi}{4}0.3^2[/tex]
[tex]A_b=0.0707m^2[/tex]
Generally the equation for Area of Hemispherical dome is mathematically given by
[tex]A_h=\frac{\pi}{2}d^2[/tex]
[tex]A_h=\frac{\pi}{2}0.3^2[/tex]
[tex]A_h=0.1414m^2[/tex]
Since base is a flat surface
[tex]F_{11}+F_{12}=1[/tex]
[tex]F_{11}=0[/tex]
Therefore
[tex]F_{12}=1[/tex]
[tex]A_b=0.0707m^2[/tex]
Generally the equation for Net rate of radiation heat transfer between two surfaces is mathematically given by
[tex]Q_{21}=-Q_{12}[/tex]
[tex]Q_{21}=\frac{\sigma(T_1^4-T_2^4)}{\frac{1-\epsilon}{A_b\epsilon_1} +\frac{1}{A_bF_{12}} +\frac{1-\epsilon_2}{A_h*\epsilon_2} }[/tex]
Where
[tex]\sigma=5.67*10^{-8}[/tex]
Therefore
[tex]65=\frac{(5.67*10^{-8}(400^4-600^4))}{\frac{1-0.55}{0.0707*0.55}+\frac{1}{0.0707}+\frac{1-\epsilon_2}{0.1414*\epsilon_2}}[/tex]
[tex]\epsilon_2=0.098[/tex]
[tex]\epsilon_2 \approx 0.1[/tex]
Therefore the emissivity of the dome is
[tex]\epsilon_2=0.098[/tex]
8. Which of Newton’s Laws would allow a passenger to fly right out of their seat if they do not have a seat belt on and a
car suddenly stops.
A) The First Law C) The Third Law
B) The Second Law D) The Fourth Law
The answer is A The first law
A child moving at constant velocity carries a 2 N ice-cream cone 1 m across a level surface. What is the net work done on the ice-cream cone?
Answer:
2 Joule
Explanation:
Work=force *dISPLACMENT
2N*1M
2 JOUL
A person carries a plank of wood 1.9 m long with one hand pushing down on it at one end with a force F1 and the other hand holding it up at 49 cm from the end of the plank with force F2. If the plank has a mass of 14 kg and its center of gravity is at the middle of the plank, what are the magnitudes of the forces F1 and F2? (The distance of 49 cm is measured from the location of F1.)
Solution :
Given :
mass of the plank, m = 14 kg
length of the plank, l = 1.9 m
Distance between [tex]$F_2$[/tex] and the end at which [tex]$F_1$[/tex] is acting, [tex]$r_2$[/tex] = 0.49 m
Torque exerted by the weight of the plank is given by :
[tex]$\tau_w= r_{\perp} \times F$[/tex]
[tex]$=-\frac{1.9}{2} \times 14 \times 9.8$[/tex]
= -130 Nm
The torque exerted by [tex]$F_1$[/tex] is
[tex]$\tau_1= r_{1} \times F_1$[/tex]
[tex]$= 0 \times F_1$[/tex]
= 0
Torque exerted by [tex]$F_2$[/tex] is
[tex]$\tau_2= r_{2} \times F_2$[/tex]
[tex]$= 0.49 \times F_2$[/tex]
[tex]$= 0.49 F_2$[/tex]
Since the system is in equilibrium, the zero rotational acceleration occurs when the net external torque on the system is zero, i.e.
[tex]$\sum \tau = 0$[/tex]
Therefore, we get
[tex]$$\sum \tau= \tau_1+\tau_2+\tau_w[/tex]
[tex]$0= 0+0.49F_2+(-130)$[/tex]
[tex]$F_2=\frac{130}{0.49}$[/tex]
= 265 N (approx)
We know that zero linear acceleration occurs when the net external force is zero on the system to achieve equilibrium, i.e.
[tex]$\sum F = 0$[/tex]
[tex]$\sum F = -F_1+F_2-mg=0$[/tex]
[tex]$F_1=F_2-mg$[/tex]
= 265 - (14 x 9.8)
= 128 N (approx)
Could someone please help me with this question?
Answer:
I linked a screen shot. The decimal version of that is:
11.03 (you want to use the positive version since you're working with area)
What is the acceleration of a car going from a starting speed of 12 m/s to 25 m/s in 6 seconds? *
Answer:
[tex]v = u + at \\ 25 = 12 + a6 \\ 13 = 6a \\ a = 2.16 \\ [/tex]
a=2.16ms^-2
a 4 kg block is moving at 12 m/s on a horizontal frictionless surface. a constant force is applied such that the block slows with an acceleration of 3 m/s^2. how much work must this force do to stop the block?
a. -576 J
b. -360 J
c. -288 J
d. 360 J
e. 576 J
The block comes to a rest from 12 m/s with acceleration 3 m/s^2, which is carried out over a distance x such that
(12 m/s)^2 - 0^2 = 2 (3 m/s^2) x
=> x = (12 m/s)^2 / (2 (3 m/s^2)) = 24 m
The force itself has a magnitude F such that
F = (4 kg) (3 m/s^2)
=> F = 12 N
This force is pointing opposite the direction in which the block is moving, so the work it's performing is negative, and the work done is
W = - (12 N) (24 m) = -288 Nm = -288 J
which makes C the answer.
what happen to the total energy of a moving object if all the applied forces are conserved
Answer:
As objects move around over time, the energy associated with them—e.g., kinetic, gravitational potential, heat—might change forms, but if energy is conserved, then the total will remain the same. Conservation of energy applies only to isolated systems.
thenks and pls mark me barinliestt :))
PLS HELP!! Our eyes perceive colors because of differences in which of the following properties of light?
Amplitude
Brightness
Wavelength
Source
Answer:
Your answer is wavelength
A bird is standing on an electric transmission line carrying 3000 A of current. A wire like this has about 3.0 x 10-5 22 of resistance per meter. The bird's feet are 6 cm apart. The bird itself has a resistance of about 4 x 105 12. The bird experiences a potential difference of 0.0054 V. What current goes through the bird?
Answer:
13.5 x 10^-9 A
Explanation:
Yes
Two loudspeakers in a plane are 2.0 m apart and in phase with each other. Both emit 700 Hz sound waves into a room where the speed of sound is 341 m/s. A listener stands 5.0 m in front of the loudspeakers and 2.0 m to one side of the center line. Is the interference at this point completely constructive, completely destructive, or in between
Answer:
interference is between destructive and constructive
Explanation:
The interference of two sound waves periodicity in phase by the speakers is
Δr = [tex]\frac{\phi }{2\pi } \ \lambda[/tex]
in this case they indicate that the frequency is f = 700 Hz, the wave speed is
v =λ f
λ = v / f
λ = 341/700
λ = 0.487 m
Let's use the Pythagorean theorem to find the distance that each wave travels
r₁ = [tex]\sqrt{x^2 + y^2}[/tex]
let's measure the distance from speaker 1
r₁ = [tex]\sqrt{5^2 + 1^2}[/tex]
r₁ = 5,099 m
the distance from the second speaker
r₂ = \sqrt{x^2 + y^2}
r₂ = [tex]\sqrt{5^2 +3^2}[/tex]
r₂= 5.831 m
the difference in the way is
Δr = r₂ -r₁
Δr = 5,831 - 5,099
Δr = 0.732 m
[tex]\frac{ \phi }{2\pi }[/tex] = Δr /λ
\frac{ \phi }{2\pi } = 0.732 / 0.487
\frac{ \phi }{2\pi } = 1.50
this is the phase difference this phase difference is approximately
Ф= [tex]\frac{\pi }{2}[/tex] =1.57,
so the interference is between destructive ( Ф = π) and constructive (Ф=2π)
A boat that can travel at 4.60 km/h in still water crosses a river with a current of 1.80 km/h. At what angle must the boat be pointed upstream to travel straight across the river
Answer:
The angle the boat must be pointed upstream is 69⁰
Explanation:
Check the image uploaded for the diagram;
Given;
speed of the boat on still water, = 4.6 km/h
speed of the boat on a river with current, = 1.8 km/h
The angle the boat must be pointed upstream is calculated as follows
[tex]tan(\theta) = \frac{4.6}{1.8} \\\\tan(\theta) = 2.556\\\\\theta = tan^{-1}(2.556)\\\\\theta = 68.63^0\\\\\theta = 69^0[/tex]
List some distinguishing features of metamorphic rocks?
Answer:
Metamorphic rocks were once igneous or sedimentary rocks, but have been changed (metamorphosed) as a result of intense heat and/or pressure within the Earth's crust. They are crystalline and often have a “squashed” (foliated or banded) texture.
Explanation:
:)
the process where water vapor into the atmosphere is changed back into liquid water
Answer:
Condensation is the process by which water vapor in the air is changed into liquid water. Condensation is crucial to the water cycle because it is responsible for the formation of clouds.
Explanation:
just is
7) The coefficient of performance (COP) of a refrigerator is defined as the ratio of A) the heat removed from the inside to the heat expelled (dismissed) to the outside. B) the heat expelled (dismissed) to the outside to the heat removed from the inside. C) the heat removed from the inside to the work done to remove the heat. D) the heat expelled (dismissed) to the outside to the work done to remove the heat
Answer:
C) the heat removed from the inside to the work done to remove the heat.
Explanation:
Refrigerator is a heat engine working in reverse direction . Heat from cold source is taken out , some work is done to remove them and total heat and work energy is thrown into outside surrounding .
If q heat is taken out and W is work done to get this heat out .
coefficient of performance ( COP ) = q / W .
Hence C ) is the right choice .
The springs of a 1500 kg car compress 5.00 mm when its 68 kg driver gets into the driver's seat. Part A If the car goes over a bump, what will be the frequency of oscillations
Answer:
the frequency of the oscillation is 1.5 Hz
Explanation:
Given;
mass of the spring, m = 1500 kg
extention of the spring, x = 5 mm = 5 x 10⁻³ m
mass of the driver = 68 kg
The weight of the driver is calculated as;
F = mg
F = 68 x 9.8 = 666.4 N
The spring constant, k, is calculated as;
k = F/m
k = (666.4 N) / (5 x 10⁻³ m)
k = 133,280 N/m
The angular speed of the spring is calculated;
[tex]\omega = \sqrt{\frac{k}{m} } \\\\\omega = \sqrt{\frac{133280}{1500} } = 9.426 \ rad/s[/tex]
The frequency of the oscillation is calculated as;
ω = 2πf
f = ω / 2π
f = (9.426) / (2π)
f = 1.5 Hz
Therefore, the frequency of the oscillation is 1.5 Hz
Two space heaters in your living room are operated at 120 V. Heater 1 has twice the resistance of heater 2. Which one will give off more heat
Answer:
Heater 2 will give off more heat.
Explanation:
The heat given off by the heaters can be found out by the following formula:
[tex]Q = VIt[/tex]
but, from Ohm's Law:
[tex]V = IR\\\\I = \frac{V}{R}[/tex]
Therefore,
[tex]Q = \frac{V^2t}{R}[/tex]
where,
Q = heat given off by the heater
V = Voltage
t = time
R = Resistance
It is clear from the equation that for a constant voltage and time, the heat given off by the heater is inversely proportional to the resistance of the heater.
Heater 2 will give off more heat.
Therefore, the heater with lower resistance will give off more heat.
A system has two possible energy states, E0 and E1 (with E1 > E0). If the difference between these energy states grows (E0 and E1 get further apart while the temperature stays constant), then the ratio of the number of particles in state E0 over the number of particles in state E1 will:__________
Answer:
The number of particles in state E0 over the number of particles in state E1 will reduce
Explanation:
E0 represents the ground level state when all the particles have same energy level.
E1 represents excited state in which only a few particle reaches
E0 and E1 get further apart means that the energy difference between the two level increases.
Thus, the number of particles in state E0 over the number of particles in state E1 will reduce.
A magnetic field of 0.27 T exists in the region enclosed by a solenoid that has 599 turns and a diameter of 9.29 cm. Within what period of time must the field be reduced to zero if the average magnitude of the induced emf within the coil during this time interval is to be 12.8 kV
Answer: [tex]8.54\times 10^{-5}\ s[/tex]
Explanation:
Given
The initial magnetic field is [tex]B=0.27\ T[/tex]
No of turns [tex]N=599\ \text{turns}[/tex]
Diameter of the solenoid [tex]d=9.29\ cm[/tex]
Induced EMF [tex]E=12.8\ kV[/tex]
Induced emf is the product of no of turns and rate of change of flux.
[tex]\Rightarrow E=-N\cdot \dfrac{\Delta \phi }{\Delta t}\\\\\Rightarrow E=-N\cdot \dfrac{\Delta (B\cdot A)}{\Delta t}\\\\\Rightarrow E=-NA\cdot \dfrac{\Delta B}{\Delta t}\\\\\text{Insert the values}\\\\\Rightarrow 12.8=-599\times \pi r^2\cdot \dfrac{(0-B)}{\Delta t}\\\\\Rightarrow \Delta t=\dfrac{599\times \pi \times (4.64\times 10^{-2})\times 0.27}{12.8\times 10^3} \\\\\Rightarrow \Delta t=854.71\times 10^{-7}\ s\\\\\text{Taking absolute value}\\\Rightarrow \Delta t=8.54\times 10^{-5}\ s[/tex]
Why do we never notice quantization?
a. because the fundamental quanta are so large
b. because the fundamental quanta are so small
C. because we are moving quickly relative to such objects
d because we are moving slowly relative to such objects
Answer:
B
Explanation:
quantization of energy is only seen in atoms
What is the formula for converting the Celsius to Fahrenheit scale?
In the circuit above, V=16 volts, R1=8 Ohms, R2=4 Ohms, and R3=7 Ohms. What is the total current I in the circuit? Answer to the nearest 0.001 Amps
Answer:
haven't heard anything back yet but I don't think we can make that work at I have been trying the new year and the researcher say hi u ok will do I have to work tomorrow
Activity 4: Caste System - The Hierarchy
Instruction: Label the hierarchy of the caste system. Write your answer on the
space provided.
An electrical insulator is a material that:
A) contains no charge
B) does not allow electrons to flow
C) has more protons than electrons
D) must be a crystal
Answer:
Option B is appropriate for this question
A given container of 5.0 kg of water maintains a constant temperature over 24 hours. If its mass doesn't change, what statements would support identifying it as a closed system.
I. Only energy was exchanged with its surroundings.
II. Its mass was constant because the water lost to evaporation was replaced with an equal volume of water.
III. It didn't exchange matter or energy with its environment.
IV. External work was used to maintain its internal energy.
A) III
B) l and III
C) II and IV
D) I and IV
Answer:
D) I and IV
Explanation:
A closed system is the one where mass can not enter or leave the system, while the energy can enter o leave the system.
I. This is true according to the definition. Because only energy can enter or leave a closed system.
II. This is not true. Because mass interaction is not allowed in a closed system.
III. This is false. Because energy exchange is allowed.
IV. True. Because energy exchange is possible.
Therefore the correct option is:
D) I and IV
True False: Marke each statement as true or false.
shift
1. Light intensity affects the rate of photosynthesis.
in
2. Energy is required by all organisms for life.
3. The ability of a plant to repair tissue depends on respiration.
4. The gas needed for photosynthesis is carbon dioxide (CO2).
5. Plants only carry on photosynthesis, not respiration.
6. Respiration can occur without photosynthesis.
Answer:
1) true 2) true 3) true 4) true 5) false 6) false
Explanation:
If two hot-air balloons are filled at the same time, but one filled with warm air and one is filled with hot air, which balloon will wise higher?
Please explain thank you! :))
hot air
Explanation: why cause doesn't every hot air balloon run on hot air
The diagram below shows a person swinging a hammer.
Which position has the least amount of kinetic energy?
A-1
B-2
C-3
D-4
True or False? To observe physical properties in matter, the matter must change into a new substance.
A sphere has a surface uniformly charged with 3.30 C. At what distance from its center is the potential 4.50 MV
Answer:
r = 6.6 x 10³ m = 6600 m
Explanation:
The potential at a distance from a charged sphere can be given as follows:
[tex]V = \frac{kq}{r}\\\\r = \frac{kq}{V}[/tex]
where,
r = distance = ?
k = Colomb Constant = 9 x 10⁹ Nm²/C²
q = charge on sphere = 3.3 C
V = potential = 4.5 MV = 4.5 x 10⁶ V
Therefore,
[tex]r = \frac{(9\ x\ 10^9\ Nm^2/C^2)(3.3\ C)}{4.5\ x\ 10^6\ V}[/tex]
r = 6.6 x 10³ m = 6600 m