Homework Clinic
Science Clinic => Physics => Topic started by: jake on Jul 27, 2018
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Consider a star with 2 planets. The mass of planet A is the same as the mass of planet B. The orbit of Planet A is on average, closer to the star than the orbit of Planet B. Which of the following statements is true?
A) Planet A moves with the same speed as Planet B.
B) Planet A is, on average, moving slower than Planet B.
C) The relative orbital speeds depend on the masses of the planets.
D) Planet A is, on average, moving faster than Planet B.
Question 2
Briefly describe the two key pieces of evidence that support the Big Bang theory.
What will be an ideal response?
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Answer to Question 1
D
Answer to Question 2
The two key pieces of evidence that support the Big Bang theory are the cosmic microwave background radiation and the observed helium content of the universe. (1 ) The cosmic background radiation consists of photons arriving at Earth directly from the end of the era of nuclei. The Big Bang predicts that this radiation came from the heat of the universe and should have a thermal radiation spectrum with a peak wavelength corresponding to 3,000 K, the temperature the universe was at the end of that nuclei era. But because the universe has expanded by a factor of about 1,000 since that time, we observe the radiation with a peak wavelength of about a millimeter, corresponding to a temperature of 2.73 K. (2 ) The Big Bang theory predicts that the universe should have a composition of 75 percent hydrogen and 25 percent helium. by mass, due to fusion reactions occurring during the era of nucleosynthesis. The Milky Way's helium fraction is about 28 percent, and no galaxy has a helium fraction lower than 25 percent. This supports the primordial helium abundance predicted by the Big Bang.