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iren [92.7K]
2 years ago
13

during a cold winter day, wind at 42 km/h is blowing parallel to a 6-m-high and 10-m-high wall of a house. If the air outside is

at 5 degrees C and the surface temperature of the wall is 12 degrees C, determine the rate of heat loss from that wall by convection. What would your answer be if the wind velocity was doubled?

Physics
1 answer:
Arturiano [62]2 years ago
4 0

Answer: 9.08KW and 16.21KW

Explanation:

The convection over a flat surface with a length of 10 m and a width of 6m.

The mean temperature is (5oC + 12oC)/2 = 8.5oC.

Then find the following properties of air at this temperature from Table A-15:

k = 0.02428 W/m(oC, v= 1.413x10-5 m2/s, and Pr = 0.7340.

find the Reynolds number. Re= VL/v

Check screenshot

This means that the flow becomes turbulent over the plate and we can use the Nusselt number equation for combined laminar and turbulent flow.

Check screenshot

We then use this Nusselt number to find the heat transfer coefficient and the heat transfer.

Check the screen shot for the calculation

Ans

9.08 kW

Then if the wind velocity were doubled, the Re number would be doubled and we would repeat the calculations above, starting with this revised Reynolds number..

Ans

16.21 kW

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Answer:

To both observers, the land opposite them is moving to the right.

Explanation:

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2 years ago
A very long conducting tube (hollow cylinder) has inner radius a and outer radius b. It carries charge per unit length +α, where
patriot [66]

Answer:

A) i) E =α/ [2πrL(εo)]

ii) E=0

iii) E = α/(πrεo)

The graph between E and r for the 3 cases is attached to this answer ;

B) i) charge on the inner surface per unit length = - α

ii) charge per unit length on the outer surface = 2α

Explanation:

A) i) For r < a, the charge is in the cavity and takes a shape of the cylinder. Thus, applying gauss law;

EA = Q(cavity) / εo

Now, Qcavity = αL

So, E(2πrL) = αL/εo

Making E the subject of the formula, we have;

E =α/ [2πrL(εo)]

ii) For a < r < b; since the distance will be in the bulk of the conductor, therefore, inside the conductor, the electric field will be zero.

So, E=0

iii) For r > b; the total enclosed charge in the system is the difference between the net charge and the charge in the inner surface of the cylinder.

Thus, Qencl = Qnet - Qinner

Qinner will be the negative of Qnet because it should be in the opposite charge of the cavity in order for the electric field to be zero. Thus;

Qencl = αL - (-αL) = 2αL

Thus, applying gauss law;

EA = Qencl / εo

Thus, E = Qencl / Aεo

E = 2αL/Aεo

Since A = 2πrL,

E = 2αL/2πrLεo = α/(πrεo)

B) i) The charge on the cavity wall must be the opposite of the point charge. Therefore, the charge per unit length in the inner surface of the tube will be - α

ii)Net charge per length for tube is +α and there is a charge of - α on the inner surface. Thus charge per unit length on the outer surface will be = +α - (- α) = 2α

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1 year ago
A steady circular __________ light means drivers must stop at a marked stop line.
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B. red................
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2 years ago
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A 125-g metal block at a temperature of 93.2 °C was immersed in 100. g of water at 18.3 °C. Given the specific heat of the metal
Nataly_w [17]

Answer:

34.17°C

Explanation:

Given:

mass of metal block = 125 g

initial temperature T_i = 93.2°C

We know

Q = m c \Delta T   ..................(1)

Q= Quantity of heat

m = mass of the substance

c = specific heat capacity

c = 4.19 for H₂O in J/g^{\circ}C

\Delta T = change in temperature

Now

The heat lost by metal = The heat gained by the metal

Heat lost by metal = 125\times 0.9\times (93.2-T_f)

Heat gained by the water = 100\times 4.184\times(T_f -18.3)

thus, we have

125\times 0.9\times (93.2-T_f) = 100\times 4.184\times(T_f -18.3)

10485-112.5T_f = 418.4T_f - 7656.72

⇒ T_f = 34.17^oC

Therefore, the final temperature will be = 34.17°C

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Alexus [3.1K]

Answer:

θ₂ = 90° - θ₁

Explanation:

When the light falls on a mirror it bounces back. This is know as reflection. The incident angle is equal to the angle of reflection.

Here, the light strikes the mirror at an angle = θ₁

To find the angle of reflection we first need to understand angle of incidence. The angle of incidence is the angle made between the incident ray and normal. Normal is an imaginary line drawn perpendicular line on the boundary of the mirror.

Since the light strikes the mirror at angle of θ₁, which is the angle between light ray and the mirror.

Angle of incidence = 90° - θ₁.

Thus, angle of reflection, θ₂ = 90° - θ₁

3 0
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