Select the correct formula for Newton's law of universal gravitation.

There are two masses present, m1 and m2, the distance between their centres of gravity is r.

Select the correct formula for Newton's law of universal gravitation.

There are two masses present, m1 and m2, the distance between their centres of gravity is r.

Select the correct option.

Which force exists between two ships with masses of \(m_1=500ton \) and \(m_2=1000ton \) when the distance between their centres of mass is 20m?

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1 ton = 1000kg

\(F = {G\times m_1\times m_2\over r^2}={6.67\times10^{-11}\times500000\times100000\over 10^2}\approx0.03N\)

Calculate the average distance of the Earth from the Sun.

\(m_{Sun}\approx2\times10^{30}kg\)

\(m_{Earth}\approx5.97\times10^{24}kg\)

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Gravity is the cause of the centripetal force, so these two forces are equal:

\({G\times m_{Earth}\times m_{Sun}\over r^2}={m_{Earth}\times v^2_{Earth}\over r}\)

The speed of the Earth can be expressed using the time it takes to orbit: \(v={2\pi r\over T}\), so

\({G\times m_{Sun}\over r^2}={(2\pi r)^2\over T^2r}\), therefore, \(r=({G\times m_{Sun}\times T^2\over(2\pi)^2})^{1/3}\approx 1.49\times 10^{11}m\)

Sun has a radius of \(7.0 \times 10^8m\) and a serface temperature of 6000K. Calculate the power output of the Sun.

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Sun has a radius of \(7.0 \times 10^8 m\) and a luminosity of \(4.52\times10^{26}W \).Calculate the surface temperature of a star of radius \(20.0 \times 10^8 m\) with the same luminosity as the Sun.

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The surface temperature pf P Cygni is 18700K. Calculate the peak wavelengh in the spectrum of this star.

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The Hertzsprung-Russell diagram is shown on the picture below. Select the digit that shows the main sequence.

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The Hertzsprung-Russell diagram is shown on the picture below. Select the digit that shows white dwarfs.

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The Hertzsprung-Russell diagram is shown on the picture below. Select the digit that shows giants.

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The Hertzsprung-Russell diagram is shown on the picture below. Select the digit that shows supergiants.

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Supergiants lay in the top of the Hertzsprung-Russell diagram.