Which of the following can be caused by lightning or arson?

g The electric power needs of a community are to be met by windmills with 40-m-diameter rotors. The windmills are to be located

Ksenya-84 [330]

Answer:

Explanation:

Given Data

The diameter of the wind mills is d = 40m

Velocity of the air is V = 6 m / s

Required power output is: P ₀ = 2100 k W

Expression to calculate the exergy of the air is

E = V ² / 2

Substitute the value in above expression

E = ( 6 m / s ) ² / 2

E = 18 m ² / s ² x (1kJ/kg / 1000m²/s²)

E = 0.018 k J / k g

Expression to calculate the density of the air is

P v =m R T

m /v = P /RT ⋯ ⋯( I )

Here

m is the mass of the air,

v is the volume of the air,

P is the atmospheric pressure,

T is the standard temperature at the atmospheric pressure and

R is the gas constant

As the density is

ρ = m /V

Substitute the value in expression (I)

ρ = 101 kP a /( 0.287 k J / k g ⋅ K ) ( 298 K )

ρ = 1.180 k g / m ²

Expression to calculate the mass flow rate is

m = ρ A V ⋯ ⋯ ( I I )

Here A is the area of the windmill

Expression to calculate the A is

A = π /4 d ²

Substitute the value in above expression

A = π /4 ( 40 m ²)

A = 1256.63 m ²

Substitute the value in expression (II)

m = ( 1.180 k g / m ³) ( 1256.63 m ²) ( 6 m / s )

m = 8896.94 k g / s

Expression to calculate the maximum power available to the windmill is

P w = m ( V ² /2 )

Substitute the value in above expression

P w = 8896.94 k g / s ( (6m/s)²/2 )

P w = 160144.92 W × ( 1 W /1000 k W )

P w = 160.144 k W

Expression to calculate the number of windmills required is

n = P o /P w

Substitute the value in above expression

n=2100kw/160.144kw

n=13.11

8 0

4 years ago

A girl and a boy are riding on a merry go round that is turning at a constant rate. The girl is near the outer edge, and the boy

galina1969 [7]

Answer:

The girl has greater tangential acceleration

Explanation:

The angular acceleration ( $\alpha$ ) of the merry go round is equal to the rate of the change of the angular velocity, $\omega$ :

$\alpha = \frac{d\omega}{dt}$

Since all the points of the merry go round complete 1 circle in the same time, the angular velocity of each point of the merry go round is the same, and so all the points also have the same angular acceleration.

The tangential acceleration instead is given by

$a_t = \alpha r$

where

$\alpha$ is the angular acceleration

r is the distance from the centre of the merry go round

Since the girl is near the outer edge and the boy is closer to the centre, the value of r for the girl is larger than for the boy, so the girl has greater tangential acceleration.

5 0

3 years ago

HELPPPPPPPP PLSSSSSSSS A car moves with constant velocity along a straight road. Its position is x1 = 0 m at t1 = 0 s and is x2

yawa3891 [41]

Answer:

Explanation:

6.2 miles

6 0

3 years ago

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Which statement is true about effective nuclear charge?a. Effective nuclear charge decreases as we move to the right across a ro

MissTica

Answer:

Option b. Effective nuclear charge increases as we move to the right across a row in the periodic table

Explanation:

The effective nuclear charge is a measure of how strong the protons in the nucleus of an atom attract the outermost electrons of such atom.

The effective nuclear charge is the net positive charge experienced by valence electrons and is calculated (as an approximation) by the equation: Zeff = Z – S, where Z is the atomic number and S is the number of shielding electrons.

The shielding electrons are those electrons in between the interesting electrons and the nucleus of the atom.

Since the shielding electrons are closer to the nucleus, they repel the outermost electrons and so cancel some of the attraction exerted by the positive charge of the nucleus, meaning that the outermost electrons feel less the efect of attraction of the protons. That is why in the equation of Zeff, the shielding electrons (S) subtract the total from the atomic number Z.

The effective nuclear charge, then, is responsible for some properties and trends in the periodic table. Here, you can see how this explains the trend of the atomic radius (size of the atom) accross a row in the periodic table.

As the effective nuclear charge is larger, in a same row of the periodic table, the shielding effect is lower, the outermost electrons are more strongly attracted by the nucleus, and the size of the atoms decrease. That is why as we move to the right in the periodic table, the size of the atoms decrease.

3 0

3 years ago

PLEASE HELP WILL GIVE BRAINLEST

mart [117]

1. Meiosis has 2 cell divisions but mitosis has only one cell division. Meiosis I is same as mitosis because parent cell produces diploid cells. But the difference between meiosis and mitosis is after the complete process meiosis produces genetically different haploid daughter cells and mitosis produces genetically same diploid daughter cells.

2. The main advantage of the sexual reproduction is It helps to produce offspring which can be well adapted to the environmental conditions due to the genetically differentiations. Hence, there are various types of offspring in the population. But the disadvantage is it requires two parents and it requires more time than asexual reproduction.

3. Advantages of asexual reproduction are it requires only parent, time for the process is relatively low, it produces genetically identical offspring. The main disadvantage is due to the production of genetically identical offspring, the survival rate is low when there is a disaster.

4. The organism can do either sexual reproduction or asexual reproduction to produce offspring. If it is difficult to find a partner to mate, the living being can do asexual reproduction to make offspring in a short period of time. When the organism needs genetically different offspring for survival, they can do sexual reproduction.

7 0

3 years ago

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