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JEE Main 2020 (9 Jan, Shift 2) · Escape Velocity

Escape Velocity question from JEE Main 2020 (9 Jan, Shift 2)

Q56JEE Main 2020 · 9 JAN · SHIFT 2Easy

Escape Velocity

Planet A has mass M and radius R. Planet B has half the mass and half the radius of Planet A. If the escape velocities from the Planets A and B are vA and vB, respectively, then vAvB=n\frac{v_A}{v_B} = n 44. The value of n is:

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Answer: (c)

  1. Escape speed v=2GMRv = \sqrt{\frac{2GM}{R}}, so v∝M/Rv \propto \sqrt{M/R}.
  2. Planet B: M/2R/2=MR\frac{M/2}{R/2} = \frac{M}{R}, same as planet A.
  3. So vA=vBv_A = v_B, i.e. vAvB=1=n4\frac{v_A}{v_B} = 1 = \frac{n}{4}.
  4. So the answer is (c) n=4n = 4.
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