JEE Main 2023 · 12 April · morning · Single correct · +4 / −1

The ratio of escape velocity of a planet to the escape velocity of earth will be:-
Given: Mass of the planet is 16 times mass of earth and radius of the planet is 4 times the radius of earth.

  1. (a) 1: 4
  2. (b) 1: √2
  3. (c) 4: 1
  4. (d) 2: 1
Answer and solution

Answer (d) 2: 1

Solution

Physics sir · 3 steps

Escape velocity goes as the square root of M over R, so take the ratio and let G cancel.

  1. Escape velocity formula. For a planet of mass M and radius R, the escape velocity from its surface is vₑ = √(2GM/R). Only M and R change from planet to planet.

    vₚ/vₑ = √(Mₚ/Mₑ×Rₑ/Rₚ)

  2. Put in numbers. Mₚ/Mₑ = 16 and Rₑ/Rₚ = 1/4. So vₚ/vₑ = √(16 × 1/4) = √4 = 2.
  3. So. The planet's escape velocity is twice the earth's, a ratio of 2 : 1, which is option (d).

The idea to keep. Escape velocity depends on √(M/R). Form the ratio first, cancel 2G, and do not forget the square root at the end.

Answer from the NTA final answer key. Solution by PrepWiser.

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Asked about 160 times in JEE Main since 2020. This question is from 2023.