Question

The nearest star visible on Earth beyond the Sun is Alpha Centauri. Its distance is 4.2 ly. If light travels 3.0 x 10^8 m/s, how far is this star from Earth in meters?

In the next 30.0 s, the Earth will travel roughly 885 km along its orbit around the Sun. Compute its average orbital speed in m/s.

If light travels 3.0 x 108 m/s, how much time does it take to travel a. one foot b. one meter c. one mile

If light travels 3.0 x 108 m/s, how far back in time are we looking when we see the Moon (distance 3.84 x 108 m)?

Answer #1

**Part 1:**

The nearest star visible on Earth beyond the Sun is Alpha Centauri. Its distance is 4.2 ly. Distance travelled by the light in 4.2 light years =

Distance = speed * time

Distance = 9.462*10^{12} * 4.2 = 39.74*10^{12}
km x 1000 = **39.74*10 ^{15} meters**

**Part 2:**

Average orbital speed in m/s = distance / time

= (885*1000)/30 = **29500 m/s**

**Part 3:**

A : 1 foot = 0.3048 meter

Time = distance / speed

= 0.3048 / 3.0*10^{8} = **0.1016*10 ^{-8}
seconds**

B: Time = distance / speed = 1/ 3.0*10^{8} =
**0.33*10 ^{-8} seconds**

C: 1 mile = 1609.34 meter

Time = distance / speed = 1609.34/ 3.0*10^{8} =
**5.354*10 ^{-6} seconds**

**Part 4:**

Time = distance / speed = 3.84*10^{8}/
3.0*10^{8} = **1.28 seconds**

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