The Sun rotates about the center of the Milky Way Galaxy at adistance of about 3

Question

The Sun rotates about the center of the Milky Way Galaxy at adistance of about 30,000 light years from the center (1yr = 9.5 x10^15 m). If it takes about 200 million years to make one rotation,estimate the mass of our galaxy. Assume that the mass distributionof our galaxy is concentrated mostly in a central uniform sphere.If all the stars had about the mass of our Sun (2 x 10^30 kg), howmany stars would there be in our galaxy?
* Use Kepler's laws and the period of the Moon (27.4 d)to determine the period of an artificial satelite orbiting verynear the Earth's surface. * The asteroid Icarus, though only a few hundred metersacross, orbits the Sun like the other planets. Its period is about410 d. What is its mean distance from the Sun? The Sun rotates about the center of the Milky Way Galaxy at adistance of about 30,000 light years from the center (1yr = 9.5 x10^15 m). If it takes about 200 million years to make one rotation,estimate the mass of our galaxy. Assume that the mass distributionof our galaxy is concentrated mostly in a central uniform sphere.If all the stars had about the mass of our Sun (2 x 10^30 kg), howmany stars would there be in our galaxy?
* Use Kepler's laws and the period of the Moon (27.4 d)to determine the period of an artificial satelite orbiting verynear the Earth's surface. * The asteroid Icarus, though only a few hundred metersacross, orbits the Sun like the other planets. Its period is about410 d. What is its mean distance from the Sun?

Explanation / Answer

Mass of galaxy is obtained by using Kepler's thirdlaw                      T2 = (42r3 / GM)                  M = (42r3 / GT2) Substitute r = 30000 * 9.5 x 1015 m                 T = 200 million years                 G = 6.67x10-11Nm2/Kg2 Solve this you get mass of galaxy.                     M = ........... The number of stars in the galaxy N = M / 2 x1030   =   ........... Solve this you get mass of galaxy.                     M = ........... The number of stars in the galaxy N = M / 2 x1030   =   ...........

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