Question:

If a planet has twice the mass of earth and three times the radius $(R)$ of earth, then the escape velocity of the planet is ($\upsilon_e$ = escape velocity of earth)

Updated On: Jun 7, 2022
  • $\sqrt{ \frac{1}{2}} \upsilon_e$
  • $\sqrt{ \frac{2}{3}} \upsilon_e$
  • $\sqrt{2} \upsilon_e$
  • none of these
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The Correct Option is B

Solution and Explanation

Escape velocity,$\upsilon_e = \sqrt{2gR}$
$ = \sqrt{\frac{2GM}{R^2}} R$ $\left( \because \:\: g = \frac{GM}{R^2} \right)$
$\therefore \:\: \upsilon_e \propto \sqrt{\frac{M}{R}}$ ...(i)
Given, $M_p = 2M$ and $R_p = 3R$
$\therefore \:\:\: (\upsilon_e)_p = \sqrt{\frac{2}{3}} \upsilon_e$ (Using (i))
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Concepts Used:

Gravitation

In mechanics, the universal force of attraction acting between all matter is known as Gravity, also called gravitation, . It is the weakest known force in nature.

Newton’s Law of Gravitation

According to Newton’s law of gravitation, “Every particle in the universe attracts every other particle with a force whose magnitude is,

  • F ∝ (M1M2) . . . . (1)
  • (F ∝ 1/r2) . . . . (2)

On combining equations (1) and (2) we get,

F ∝ M1M2/r2

F = G × [M1M2]/r2 . . . . (7)

Or, f(r) = GM1M2/r2

The dimension formula of G is [M-1L3T-2].