Question

Suppose a star is 4.40 ✕ 10¹⁸ m from Earth. Imagine a pulse of radio waves is emitted toward Earth from the surface of this star. How long (in years) would it take to reach Earth?

The Sun is 1.50 ✕ 10¹¹ m from Earth. How long (in minutes) does it take sunlight to reach Earth?

The Moon is 3.84 ✕ 10⁸ m from Earth. How long (in s) does it take for a radio transmission to travel from Earth to the Moon and back?

Answer 1

here speed of waves and light is 3e8 m/s

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time = distance / speed

so,

Suppose a star is 4.40 ✕ 10¹⁸ m from Earth. Imagine a pulse of radio waves is emitted toward Earth from the surface of this star. How long (in years) would it take to reach Earth?

t = 4.40e18 / 3e8

t = 1.466e10 seconds

or

t = 465 years

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The Sun is 1.50 ✕ 10¹¹ m from Earth. How long (in minutes) does it take sunlight to reach Earth?

t - 1.5e11 / 3e8

t = 500 seconds

or

t = 8.333 minutes

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The Moon is 3.84 ✕ 10⁸ m from Earth. How long (in s) does it take for a radio transmission to travel from Earth to the Moon and back?

be careful, here distance is to and fro

so,

t = 2d / v

t = 2 * 3.84e8 / 3e8

t = 2.56 seconds