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Wave Optics

Question
CBSEENPH12039784

The ratio of escape velocity at earth (Ve) to the escape velocity at a planet (vp) whose radius and mean density are twice as that of earth is,

  • 1:2 square root of 2

  • 1:4

  • 1:square root of 2

  • 1:2

Solution

A.

1:2 square root of 2

Escape velocity of earth can be given as,
vesquare root of 2 gR end root = Rsquare root of 8 over 3 πGρ end root, where straight rho is the density of the earth.
rightwards double arrow space straight v subscript straight e space equals space straight R square root of 8 over 3 πGρ end root  ... (i)
Given that the radius and mean density of planet are twice as that of earth.
So, escape velocity at planet will be,
straight v subscript straight p space equals space 2 straight R space square root of 8 over 3 πG 2 straight rho end root space space space... space left parenthesis ii right parenthesis
Dividing space eqn. space by space left parenthesis straight i right parenthesis space by space left parenthesis ii right parenthesis comma
straight v subscript straight e over straight v subscript straight p space equals space fraction numerator straight R square root of 8 over 3 πGρ end root space over denominator 2 straight R square root of 8 over 3 πG 2 straight rho end root end fraction
rightwards double arrow space straight v subscript straight e over straight v subscript straight p space equals fraction numerator 1 over denominator 2 square root of 2 end fraction