Question

12. Laser pulses can be timed as they bounce off mirror-reflectors left on the Moon by astronauts, in order to calculate the Earth-Moon distance to the nearest centimeter — a process called “lunar ranging.” (The Moon's orbit is not a perfect circle, so its distance from Earth varies by approx. 10% during each orbit.) Suppose, on a particular day, that the laser beam takes 2.50 s to complete the round trip. What is the Earth-Moon distance on that day? A. 3.35 x 10 km B. 3.45 ~ 10 km C. 3.55 x 10ʻ km D. 3.65 ~ 10 km E. 3.75 ~ 10 km

Answer 1

DISTANCE = velocity of light (c) * time taken (t)

  as 2.5s is for a round trip we need to half it to get distance i.e. t = 2.5/2 = 1.25 s

Velocity of light (c) =3*10^8 m/s

distance = 3*10^8 * 1.25 = 3.75*10^8 m = 3.75*10^5 km

Hence E is correct

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