The Astronomical Unit

Classical Mechanics Level 2

About how many miles is our sun away from planet Earth?

You may use the fact that

  • The speed of light is approximately 3 × 1 0 8 metres/second 3\times 10^8 \text{ metres/second} , and

  • 1 mile 1\text{ mile} is equivalent to 1.609 km 1.609 \text{ km} .

  • It takes about 8 minutes for light from the sun to reach us.

93 thousand 93 million 93 billion 93 trillion

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Andrew Ellinor by Andrew Ellinor , 33, USA

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1 solution

Nihar Mahajan
Mar 29, 2016

Speed of light ( c ) ≈ 3 × 1 0 8 m / s (c)\approx 3\times 10^8 \ m/s . Time taken by light to reach earth from sun ( t ) = 8 m i n s = 8 × 60 s e c s (t)=8 \ mins = 8\times 60 \ secs .

D i s t a n c e = S p e e d ⋅ T i m e = c ⋅ t = 3 × 1 0 8 × 8 × 60 m e t e r s = 144000000000 m e t e r s ≈ 93 m i l l i o n m i l e s Distance=Speed \cdot Time=c\cdot t= 3\times 10^8 \times 8\times 60 \ meters = 144000000000 \ meters \approx 93 \ million \ miles

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Moderator note:

Simple standard approach.

Shouldn't it be 90 million?

Rishik Jain - 5 years, 2 months ago

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Can you see 90 million in the choices? If not, which is the closest to 90 million?

Nihar Mahajan - 5 years, 2 months ago

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Then shouldn't the choices be changed?

Rishik Jain - 5 years, 2 months ago

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@Rishik Jain – In fact 93 million is a more correct choice since the speed of light is not exactly 3 × 1 0 8 m / s 3\times 10^8 \ m/s , its a bit less.

Nihar Mahajan - 5 years, 2 months ago

Aren't miles the worst? :P

Andrew Ellinor - 5 years, 2 months ago

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Indeed they are! :upside down face:

Nihar Mahajan - 5 years, 2 months ago

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