JEE Main 2020 (6 Sep, Shift 2) Physics Q6: Gravitation

Question

Two planets have masses M and 16 M and their radii are a and 2a, respectively. The separation between the centres of the planets is 10a. A body of mass m is fired from the surface of the larger planet towards the smaller planet along the line joining their centres. For the body to be able to reach at the surface of smaller planet, the minimum firing speed needed is :

(1) $4\sqrt{\frac{GM}{a}}$
(2) $\frac{3}{2}\sqrt{\frac{5GM}{a}}$ Official answer
(3) $\sqrt{\frac{GM^2}{ma}}$
(4) $2\sqrt{\frac{GM}{a}}$

Official answer

Option 2

NTA final key (Sep 2020).

Accepted Answer

Option 2: $\frac{3}{2}\sqrt{\frac{5GM}{a}}$

Answer

$4\sqrt{\frac{GM}{a}}$

Answer

$\frac{3}{2}\sqrt{\frac{5GM}{a}}$

Answer

$\sqrt{\frac{GM^2}{ma}}$

Answer

$2\sqrt{\frac{GM}{a}}$

JEE Main 6 September 2020, Shift 2, Physics Q6

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