Hubble's Law: a Galaxy Is Observed Receding from Earth with a Speed

question 43

Multiple Choice

Hubble's law: A galaxy is observed receding from Earth with a speed of 2800 km/s. If the Hubble constant is 22 km/s per million light-years, estimate how many years ago the light that we presently see from the galaxy actually left the galaxy. (c = 3.00 × 10⁸ m/s, 1 ly = 9.461 × 10¹⁵ m, 1 y = 3.156 × 10⁷ s)

• A) 1.3 × 10⁸ y
• B) 4.2 × 10⁸ y
• C) 4.2 × 10⁷ y
• D) 1.4 × 10⁷ y
• E) 4.2 × 10⁶ y

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