What evidence suggests that most of the mass of the Milky Way is in the form of dark matter?
A) The orbital speeds of stars far from the galactic center are surprisingly high.
B) Although dark matter emits no visible light, we have detected its radio emissions.
C) Theoretical models of galaxy formation suggest that a galaxy cannot form unless it has at least 10 times as much matter as we see in the Milky Way disk.
D) Our view of distant galaxies is often obscured by dark blotches, which are presumably made of dark matter.
A) The orbital speeds of stars far from the galactic center are surprisingly high.
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The pin at A in Problem 3.7 is removed and the pole rests on a rough surface at A in the position shown in the figure below. The minimum coefficient of friction at A required for equilibrium is:
(A) 0.41
(B) 0.25
(C) 0.37
(D) 0.64
An H-R diagram for a globular cluster will show a horizontal branch, which is a line of stars above the main-sequence but to the left of the subgiants and red giants. Which of the following statements about these horizontal branch stars is true?
A) They have inert (nonfusing) carbon cores. B) Their sole source of energy is hydrogen shell fusion. C) They generate energy through both hydrogen fusion and helium fusion. D) In a particular star cluster, all horizontal branch stars have the same spectral type.
An aluminum rod is 10.0 cm long and a steel rod is 80.0 cm long when both rods are at a temperature of 15°C. Both rods have the same diameter. The rods are now joined end-to-end to form a rod 90.0 cm long
If the temperature is now raised from 15°C to 90°C, what is the increase in the length of the joined rod? The coefficient of linear expansion of aluminum is 2.4 × 10-5 K-1 and that of steel is 1.2 × 10-5 K-1. A) 0.90 mm B) 0.99 mm C) 0.81 mm D) 0.63 mm E) 0.72 mm
Intensity: An 8.0-mW laser beam emits a cylindrical beam of single-wavelength sinusoidal light 0.90 mm in diameter. What is the rms value of the electric field in this laser beam? (?0 = 8.85 × 10-12 C2/N ? m2, ?0 = 4? × 10-7 T ? m/A, c = 3.0 × 108 m/s)
A. 2200 N/C B. 1000 N/C C. 1100 N/C D. 4100 N/C E. 2000 N/C