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3 years ago

20. Consider two Stars A and B with temperatures Ta and TB and radii Ra and RB respectively. If TA

Physics

1 answer:

Rus_ich [418]3 years ago

4 0

Answer:

$L_A = 9 L_B$

Explanation:

The formula that relates the luminosity of a star (L) to its radius (R) and the temperature (T) is

$L=\frac{R^2}{T^4}$

For star B, we can write:

$L_B=\frac{R_B^2}{T_B^4}$

For star A, we have

$T_A = 2 T_B\\R_A = 12 R_B$

So the luminosity of star A is

$L_A=\frac{R_A^2}{T_A^4}=\frac{(12 R_B)^2}{(2 T_B)^4}=\frac{144 R_B^2}{16 T_B^4}=9\frac{R_B^2}{T_B^4}=9 L_B$

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A student throws a small rock straight upwards. The rock rises to its highest point and then falls back down. How does the speed

Vladimir [108]

Answer:

we assume that it starts with a velocity of 10m/s. At 2m height above ground level, its velocity decreases at 3m above ground level

for its way down the velocity at 3m on its way down is more than its velocity at 2m on its way down.

Explanation:

A student throws a small rock straight upwards. The rock rises to its highest point and then falls back down. How does the speed of the rock at 2m on the way down compare with its speed at 2m on the way up?

It decreases in speed on its way down and increases in speed on its way down.

it decreases in speed on its way up because the the vertical motion is against the earths gravitational pull on an object to the earth's center

.It increases in speed on his way down because its under the influence of gravity

from newton's equation of motion we can check by

using V^2=u^2+2as

we assume that it starts with a velocity of 10m/s. At 2m height above ground level, its velocity decreases at 3m above ground level

for its way down the velocity at 3m on its way down is more than its velocity at 2m on its way down.

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3 years ago

Which of the following is likely to contribute to geological events that take place on Earth?

Dennis_Churaev [7]

Crust sitting on top of Milton rock of the mantle

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3 years ago

Read 2 more answers

A person of mass 55 kg swings on a rope length 4 m from rest (when the rope makes an angle of 30 degrees with the vertical) and

vovangra [49]

Answer:

θ = 19.66°

Explanation:

To determine the angle that the rope makes with the vertical for the two people, you first take into account the potential energy of the first person before he swings on the rope:

$U=mgh$

h: distance to the ground

g: gravitational acceleration = 9.8m/s^2

m: mass of the first person = 55 kg

In the image attache below you can notice that the height h is:

$h=4-4cos(30\°)=0.53m$

Then, the potential energy is:

$U=(55kg)(9.8m/s^2)(0.53m)=285.67J$

When the first person picks up the second person (when the rope is exactly vertical), all the potential energy becomes kinetic energy. Next, when both people reaches the maximum height h' the energy must be equal to the initial potential energy of the first person:

$U'=(m_1+m_2)gh'=285.67\ J$

From the previous equation you can get h':

$h'=\frac{285.67J}{(55kg+70kg)(9.8m/s^2)}=0.2332m$

Finally, you obtain the angle between the rope at the height h,' and the vertical, by calculating the following:

$h'=4-4cos(\theta)\\\\\theta=cos^{-1}(\frac{4-h'}{4})=cos^{-1}(\frac{4-0.2332}{4})=19.66\°$

hence, the angle between the rope and the vertical, when the two people are in the rope is 19.66°

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3 years ago

Which statement correctly describes the current in a circuit that is made up of any two resistors connected in series with a bat

Aleksandr-060686 [28]

The answer is D. The current in the battery and in each resistor is the same.

If we have two or more components in series, the current that flows through each of them is the same.

In this case, the battery generates the current, and since there must be conservation of electric charge, no current can be lost through the resistors.

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3 years ago

The current atmospheres of the terrestrial planets were formed when the planets formed

Alexus [3.1K]

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3 years ago