The Earth currently has an orbital period of 1 year and a semi-major
axis length of 1 AU. If the Earth's orbit changed and the semi-major
axis length increased to 1.1 AU, how would the Earth's orbital period change?

A: It would increase by 0.15 years

B: It would increase by 0.032 years

C: It would decrease by 0.15 years

D: It would decrease by 0.032 years

Respuesta :

The Earth's orbital period change is A: It would increase by 0.15 years

Using Kepler's third law which states that the square of the orbital period of the planet is directly proportional to the cube of its distance from the sun.

So, T² ∝ R³

T'²/T² = R'³/R³ where

  • T = orbital period at R = 1 year
  • R = initial axis length = 1 AU
  • T' = orbital period at R'
  • R' = final axis length = 1.1 AU.

So, making T' subject of the formula, we have

T' = [√(R'/R)³]T

T' = [√(1.1 AU/1 AU)³] × 1 year

T' = [√(1.1)³] × 1 year

T' = √1.331 × 1 year

T' = 1.15 × 1 year

T' = 1.15 years.

So, the change in the Earth's orbital period ΔT = T' - T

= 1.15 years - 1 year

= 0.15 years

Since this is positive, the orbital period increases by 0.15 years.

So, the Earth's orbital period change is A: It would increase by 0.15 years

Learn more about Kepler's third law here:

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