What would be the duration of the year if the distance between the Earth and sun has been increased by two times its present distance?

What would be the duration of the year if the distance between the Earth and sun has been increased by two times its present distance?

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Concept:

  • Kepler's Law of Planetry Motion: When a planet is revolving around its star (Sun for earth), then the square of the time period of revolution is directly proportional to the cube of the radius of revolution.

T2 ∝ R3

⇒ T2 = k R3

  • The time period of the revolution of the earth across the sun is one year.
  • One year of the earth consists of 365 days.

Calculation:

Let a present, time period of revolution is 

T = 365 days -- (1)

The radius of earth R

By Kepler's Law

T2 = k R3 -- (2)

If the radius is halved then the new radius is R', and the new time period is T' 

Radius is halved

 \(R'=\frac{R}{2}\)---- (3)

T'2 = k R'3 

⇒ \(T'^2 = k(\frac{R}{2})^3\)

⇒ \(T'^2 = k(\frac{R^3}{8})\) --- (4)

Equation (3) in (4)

\(T'^2 = k(\frac{R^2}{8})\)

⇒ \(T' = (\frac{T}{\sqrt{8}})\) (using eq 2 )

⇒ \(T' = (\frac{365}{\sqrt{8}})\)

⇒ T' = 129 

So, 129 days is the correct answer.

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What would be the duration of the year if the distance between the Earth and sun has been increased by two times its present distance?

Text Solution

1032 days 365 days 129 days 556 days

Answer : A

Solution : By Kepler's second law, `T^(2)prop r^(3)` <br> `therefore ((T_(2))/(T_(1)))^(2)=((r_(2))/(r_(1)))^(3)=((2)/(1))^(3) = 8` <br> `therefore (T_(2))/(T_(1))=sqrt(8)=2sqrt(2) " " therefore T_(2)=2sqrt(2)xx T_(1)` <br> `therefore T_(2)=365xx2xx1.414=1032` days