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3 years ago

What does the term Hubble time mean in cosmology, and what is the current best calculation for the Hubble time?

1 answer:

4 0

Hubble time in cosmology means the estimated age of the universe and the best calculation for it is T=1/H, where H is the Hubble constant

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a flag of mass 2.5 kg is supported by a single rope. A strong horizontal wind exerts a force of 12 N on the flag. Calculate the

tatuchka [14]

The free-body diagram of the forces acting on the flag is in the picture in attachment.

We have: the weight, downward, with magnitude
$W=mg = (2.5 kg)(9.81 m/s^2)=24.5 N$
the force of the wind F, acting horizontally, with intensity
$F=12 N$
and the tension T of the rope. To write the conditions of equilibrium, we must decompose T on both x- and y-axis (x-axis is taken horizontally whil y-axis is taken vertically):
$T \cos \alpha -F=0$
$T \sin \alpha -W=$
By dividing the second equation by the first one, we get
$\tan \alpha = \frac{W}{F}= \frac{24.5 N}{12 N}=2.04$
From which we find
$\alpha = 63.8 ^{\circ}$
which is the angle of the rope with respect to the horizontal.

By replacing this value into the first equation, we can also find the tension of the rope:
$T= \frac{F}{\cos \alpha}= \frac{12 N}{\cos 63.8^{\circ}}=27.2 N$

7 0

3 years ago

Light in vacuum is incident on the surface of a slab of transparent material. In the vacuum the beam makes an angle of 39.9° wit

wariber [46]

Answer:

n=2.053

Explanation:

We will use Snell's Law defined as:

$n_{1}*Sin\theta_{1}=n_{2}*Sin\theta_{2}$

Where n values are indexes of refraction and $\theta$ values are the angles in each medium. For vacuum, the index of refraction in n=1. With this we have enough information to state:

$1*Sin(39.9)=n_{2}*Sin(18.2)$

Solving for $n_{2}$ yields:

$n_{2}=\frac{Sin(39.9)}{Sin(18.2)}=2.053$

Remember to use degrees for trigonometric functions instead of radians!

6 0

2 years ago

What assumption can be made about the densities of two different spheres that have

Triss [41]

Answer:

Their densities are different as well

Explanation:

Density is worked out by dividing mass by volume. If the mass was the same then the densities would be as well. But it's not.

How many marks is this question?

8 0

3 years ago

Gravitational potential energy is often released by burning substances. true or false

jolli1 [7]

Gravitational potential energy is caused when an object is resting above the ground. It is released when the object is falling, not by burning substances.

4 0

2 years ago

Read 2 more answers

Which of the following has potential but not kinetic energy?

marissa [1.9K]

A ball sitting on a shelf:)

7 0

2 years ago