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2 years ago

What causes the apparent motions of stars across the sky each night

Physics

1 answer:

densk [106]2 years ago

3 0

Answer:

Explanation:

for the motion every night, it is because the Earth spins on its axis.

for the changes over a year, this is because the Earth rotates around the sun.

for the changes over hundreds, thousands or millions of years, this is because the whole solar system (including the Earth, of course) rotates with all the other stars in our galaxy around the center of the galaxy. and each star system has its own orbit (similar to the planets in our solar system).

it is very rare to see objects outside of our galaxy without a telescope, but they change too over a long period of time, because our galaxy not only rotates by also moves through the universe, and these other objects move on their own too.

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A 50.0 Watt stereo emits sound waves isotropically at a wavelength of 0.700 meters. This stereo is stationary, but a person in a

photoshop1234 [79]

Answer:

a) f' = 432 Hz

b) I = 8.12*10^-4 W/m^2

Explanation:

a) To calculate the frequency of sound waves that car receives, you take into account the Doppler effect. In this case (observer moves away of the source) you have the following formula:

$f'=f(\frac{v-v_o}{v+v_s})$ (1)

where

f: frequency of the source = ?

v: speed of sound = 343 m/s

vo: speed of the observer = 40.0 m/s

vs: speed of the source = 0 m/s (stationary)

You replace the values of all parameters in the equation (1):

To calculate f' you first calculate the frequency of the sound wave, by using the following formula:

$v=\lambda f\\\\$

v: speed of sound

λ: wavelength = 0.700 m

$f=\frac{v}{\lambda}=\frac{343m/s}{0.700m}=480Hz$

Next, you replace the values of all parameters in the equation (1):

$f'=(490Hz)(\frac{343m/s-40.0m/s}{343m/s})=432Hz$

hence, the frequency perceived by the car is 432 Hz

b) To calculate the power of the sound wave, when the car is 70.0 maway from the speaker, you use the following formula:

$I=\frac{P}{4\pi r^2}$

P: power of the source = 50.0 W

r: distance to the source = 70.0 m

$I=\frac{50.0 W}{4\pi(70.0m)^2}=8.12*10^{-4}\frac{W}{m^2}$

hence, the intensity is 8.12*10^⁻4 W/m^2

3 0

2 years ago

Which statement about tornadoes is correct? a. They are a very common part of thunderstorms. b. Seventy-five percent of the worl

Anit [1.1K]

As strange as it may seem, around 75% world’s tornadoes

occur in the United States. It's actually because of the unique

geography of North America, and how the winds and storms

get funneled up through the US. (choice-b)

It's true that when there's a tornado, it usually comes along with a thunderstorm. But tornadoes are way way LESS common than thunderstorms.

Their main danger is from the high winds in the center of the funnel.

The rain is minor compared to the wind damage.

Tornadoes are not really the strongest storms on Earth.

Welll ... I guess that could depend on what "strong storm" means.

Sure, a tornado is incredibly vicious and powerful. But it's only a few

miles wide, and it only lasts for a few hours and then it's all over.

The tropical cyclones ... hurricanes, monsoons, typhoons ... don't have

winds as fast as tornadoes, but they can be a thousand miles wide and

last for weeks.

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3 years ago

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HClO4 is stronger acid than HClO? Give reason

mamaluj [8]

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2 years ago

A third class lever that is 5cm away from the fulcrum, and 20cm away from the fulcrum?

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2 years ago

You are going to invent a new device that people can use instead of a microwave oven to warm up leftovers. Which type of electro

kicyunya [14]

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3 years ago

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