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# Astronomy | Astrophysics Answers

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how the distance on earth are inter related where as the earth is in parabola shape?
calculate the value of acceleration due to gravity at point:
(a)5.0 km above the earths surface and
(b)5.0 km below the earths surface.Radius of earth=6400km
and the value of g at the surface of the earth is 9.80 m/s^2
The Saturn V rocket that took the first astronauts to the moon had a mass of 5 tonnes. Its stage 1 rockets fired for 6 minutes and took the rocket to an altitude of 67km. How much work did the stage 1 rockets do in this time?
the planet mars takes 1.88 years to complete on revolution around the sun. the mean distance of the earth from the sun is 1.5x1o*8 km . calculate that of planet of mars
Consider a galaxy which is 100 million light-years away. Calculate its speed (in km/s), assuming that the Hubble constant is 22 km/sec/million light-years. Enter your answer in the blank (numbers only - no units!).
A microwave has a 3cm wavelength. How many complete microwaves could you fit into a long wave radio wavelength of 1000m
A rock dropped into a well is heard to splash 2.30 seconds later. How deep is the well to the water's surface?
Assume that dwarf spherical galaxy has the so-called Plummer sphere potential Φ(r) = − (r0v02)/(sqr(r2+r02)), with constants v0 = 125 km/s, and r0 = 2.5 kpc (core radius). [This is the force per unit mass of the test particle, a.k.a. specific potential. The same way we talk about the specific force, which is simply force/mass or acceleration!] The objective is to fully characterize the system based on the potential. This is always easy in spherically symmetric systems. Find the specific force field created by specific potential Φ(r). Find asymptotic behavior of F and Φ with r at r <<r0 and at r → ∞. Note: by *behavior* we mean not only the value, but also functional form, in this case a certain power law. For example, 1/(1+x3 ) behaves like ≈ 1−x3/3 for x <<1 (first 2 terms of Taylor expansion; we can give only one leading term, but here it was so easy..), and like ∼ x −3 at large radii; the function goes to zero as the 3rd power of radius.
A sun-like star is torn apart by the tidal force (differential attraction) of a black hole of mass 1 million solar masses. It forms an accretion disk around a black hole which quickly flows into a black hole releasing 1/4 of its rest mass in the form of radiation during a time equal to one orbital period at the radius of the black hole horizon (Schwarzschild radius). What power in watts and in units of solar luminosity is emitted and for how long? Would a less massive black hole produce a smaller or larger luminosity? Is the released energy larger or smaller than the energy obtainable from the star via hydrogen fusion?
Galaxy NGC2300 has an flat disk dominating the visible light image. Surface brightness is given by
the exponential law
I(R) = I0 exp(−R/Rd)
where I0 is the central surface brightness, R distance from the center, and Rd = 4 kpc the exponential
radial scale of the disk (e-folding distance). The total luminosity of the galaxy equals L = (2.5·10^10)L(sun) .
Considering that the total luminosity is surface brightness I(R) integrated over the area of the
whole disk from R = 0 to R = ∞ (not over the radial distance, a mistake some people make!), compute
I0 (in units of L(sun) /pc^2)
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