The mass of Mars is 6 point 4 2 times 10 to the 23th power kilograms Its moon Phobos is 9378 kilometers away from Mars and has a mass of 1 point 0 6 times 10 to the 16th power kilograms What is the gravitational force between Mars and Phobos?

Use Newton’s law of gravitation, F = Gm₁m₂/r², and convert 9,378 km to 9.378 × 10⁶ m. Substituting the masses and G = 6.67 × 10⁻¹¹ gives F ≈ (6.67 × 10⁻¹¹)(6.42 × 10²³)(1.06 × 10¹⁶)/(9.378 × 10⁶)² ≈ 5.16 × 10¹⁵ N. Therefore, the force is 5.16 × 10¹⁵ newtons, choice B.

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