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worty [1.4K]
3 years ago
12

Some people wish that we lived in a recollapsing universe that would eventually stop expanding and start contracting. For this t

o be the case, which of the following would have to be true (based on current understanding)?)? (A) Dark energy is the dominant form of energy in the cosmos. (B) Dark energy does not exist and there is much more dark matter than we are aware of to date. (C) Neither dark energy nor dark matter really exist. (D) Dark energy exists but dark matter does not.
Physics
1 answer:
Monica [59]3 years ago
4 0

Answer:

(B) Dark energy does not exist and there is much more matter than current evidence suggests.

Explanation:

The repulsive force which is accelerating expansion of the universe is called as dark energy. Most of matter present in the universe is the dark matter of about eighty five percent.

So, a collapsing universe would not have the dark energy and there is more matter which is not the dark matter. This theory is rejected because expansion of the universe is observable.

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A spacecraft is moving past the earth at a constant speed of 0.60 times the speed of light. The astronaut measures the time inte
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Answer:

the time interval that an earth observer measures is 4 seconds

Explanation:

Given the data in the question;

speed of the spacecraft as it moves past the is 0.6 times the speed of light

we know that speed of light c = 3 × 10⁸ m/s

so speed of spacecraft v = 0.6 × c = 0.6c

time interval between ticks of the spacecraft clock Δt₀ = 3.2 seconds

Now, from time dilation;

t = Δt₀ / √( 1 - ( v² / c² ) )

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t = 3.2 / √( 1 - ( 0.6c / c )² )

t = 3.2 / √( 1 - ( 0.6 )² )

t = 3.2 / √( 1 - 0.36 )

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t = 4 seconds

Therefore, the time interval that an earth observer measures is 4 seconds

6 0
3 years ago
A helicopter has blades of length 4.0 m rotating at 3.0 rev/s in a horizontal plane.If the vertical component of the Earth’s mag
VARVARA [1.3K]

Answer:

Induced emf, \epsilon=9.79\times 10^7\ volts

Explanation:

Given that,

Length of the helicopter, l = 4 m

Angular speed of the helicopter, \omega=3\ rev/s=18.84\ rad/s

The vertical component of the Earth’s magnetic field is, B=6.5\times 10^5\ T

We need to find the induced emf between the tip of a blade and the hub. The induced emf in terms of angular velocity of an rotating object is given by :

\epsilon=\dfrac{1}{2}B\omega l^2

\epsilon=\dfrac{1}{2}\times 6.5\times 10^5\times 18.84\times (4)^2

\epsilon=9.79\times 10^7\ volts

So, the induced emf between the tip of a blade and the hub is \epsilon=9.79\times 10^7\ volts. Hence, this is the required solution.

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Answer:

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Which set of terms represent mechanical waves?
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