Question:

Escape velocity on a planet is \(10\ \text{km/s}\). If the radius remains same but the mass becomes \(4\) times, the new escape velocity is:

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Escape velocity depends on both mass and radius: \[ v_e \propto \sqrt{\frac{M}{R}} \] If mass becomes \(n\) times and radius remains constant, escape velocity becomes: \[ \sqrt{n}\times \text{original escape velocity} \]
Updated On: Jun 3, 2026
  • \(10\ \text{km/s}\)
  • \(20\ \text{km/s}\)
  • \(5\ \text{km/s}\)
  • \(40\ \text{km/s}\)
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The Correct Option is B

Solution and Explanation

Concept: Escape velocity is the minimum velocity required for an object to escape completely from the gravitational field of a planet without further propulsion. The formula for escape velocity is: :contentReference[oaicite:0]{index=0} where: \[ v_e = \text{escape velocity} \] \[ G = \text{gravitational constant} \] \[ M = \text{mass of the planet} \] \[ R = \text{radius of the planet} \] From the formula: \[ v_e \propto \sqrt{M} \] when radius remains constant.

Step 1:
Write the relation between old and new escape velocity. Initial escape velocity: \[ v_1=10\ \text{km/s} \] New mass: \[ M_2=4M_1 \] Since radius remains same: \[ \frac{v_2}{v_1}=\sqrt{\frac{M_2}{M_1}} \] Substitute: \[ \frac{v_2}{10}=\sqrt{\frac{4M_1}{M_1}} \] \[ \frac{v_2}{10}=\sqrt{4} \] \[ \frac{v_2}{10}=2 \] \[ v_2=20\ \text{km/s} \]

Step 2:
Write the final answer. Hence, the new escape velocity is: \[ \boxed{20\ \text{km/s}} \] Therefore, the correct option is: \[ \boxed{(B)\ 20\ \text{km/s}} \]
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