JEE MAIN - Physics (2022 - 30th June Morning Shift - No. 3)
The radii of two planets A and B are in the ratio 2 : 3. Their densities are 3$$\rho$$ and 5$$\rho$$ respectively. The ratio of their acceleration due to gravity is :
9 : 4
9 : 8
9 : 10
2 : 5
Explanation
Given,
$${{{r_A}} \over {{r_B}}} = {2 \over 3}$$
$${{{\rho _A}} \over {{\rho _B}}} = {3 \over 5}$$
We know,
Acceleration due to gravity
$$g = {{GM} \over {{r^2}}} = {G \over {{r^2}}} \times {4 \over 3}\pi {r^3} \times \rho $$
$$ = {{4\pi Gr\rho } \over 3}$$
$$\therefore$$ $$g \propto \rho r$$
$$\therefore$$ $${{{g_A}} \over {{g_B}}} = {{{\rho _A}} \over {{\rho _B}}} \times {{{r_A}} \over {{r_B}}}$$
$$ = {3 \over 5} \times {2 \over 3}$$
$$ = {2 \over 5}$$
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