a) The distance to a star is approximately 9.80 1018 m. If this star were to bur

Question

a) The distance to a star is approximately 9.80 1018 m. If this star were to burn out today, in how many years would we see it disappear? years

(b) How long does it take for sunlight to reach Mars? Your response differs from the correct answer by more than 100%. 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 11.8 km away? s

Explanation / Answer

D = 9.8 x 10^18 m

a)Speed = distance/time

time = distance/speed = D/c

t = 9.8 x 10^18/3 x 10^8 = 3.27 x 10^10 s = 1037 years

Hence, t = 1037 years

b)distance of Mars = D = 2.28 x 10^11 m

t = 2.28 x 10^11/3 x 10^8 = 760 s = 12.67 min

Hence, t = 12.67 min

c)d = 3.8 x 10^8 m/s

to and from means, D = 2d = 7.6 x 10^8 m

t = 7.6 x 10^8/3 x 10^8 = 2.53 s

Hence, t = 2.53 s

d)D = 2 pi r = 2 x 3.14 x 6.37 x 10^6 = 4 x 10^7 m

t = 4 x 10^7/3 x 10^8 = 0.133 s

t = 0.133 s

e) t = 11800/3 x 10^8 = 3.93 x 10^-5 s

Hence, t = 3.93 x 10^-5 s

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