(a) The distance to a star is approximately 4.70 1018 m. If this star were to bu

Question

(a) The distance to a star is approximately 4.70 1018 m. If this star were to burn out today, in how many years would we see it disappear? _497.13065_ years (correct) (b) How long does it take for sunlight to reach Mars? _____ minutes (c) How long does it take for a microwave radar signal to travel from Earth to the Moon and back? _____ s (d) How long does it take for a radio wave to travel once around the Earth in a great circle, close to the planet's surface? _____ s (e) How long does it take for light to reach you from a lightning stroke 9.8 km away? _____ s

Explanation / Answer

Q: a) The distance to a star is approximately 9.30 1018 m. If this star were to burn out today, in how many years would we see it disappear? (b) How long does it take for a microwave radar signal to travel from Earth to the Moon and back? in seconds (c) How long does it take for a radio wave to travel once around the Earth in a great circle, close to the planet's surface? in seconds ANS: a) t = D / v = 9.3 . 10^18 / 3 . 10^8 = 3.1 . 10^10 s = 3.1 . 10^10 / 3.1 . 10^ 7 = 1000 years b) Distance to the Moon = 3.8 . 10^8 m Distance there and back = 7.6 . 10^8 m Time taken = 7.6 . 10^8 / 3 . 10^8 = 2.53 s c) Distance around the Earth = 2 . p . 6.37 . 10^6 = 4. 10^7 m Time taken = 4. 10^7 / 3 . 10^8 = 0.133 s

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