Newton’s Law of Gravitation — A/L Physics

How do I practise Newton’s Law of Gravitation?

1 question with a worked solution

1. Two point masses m and 4m are fixed at a distance d apart in a vacuum. At what distance from the mass m along the line joining them is the net gravitational force on a third mass M equal to zero?
   1. A) d / 3
   2. B) d / 2
   3. C) 2d / 3
   4. D) d / 4
   Check my answer

   Correct answer: A) d / 3

   Let x be the distance from m. Gravitational forces from both masses must balance: G m M / x² = G (4m) M / (d - x)² => 1 / x² = 4 / (d - x)². Taking square roots: 1 / x = 2 / (d - x) => d - x = 2x => 3x = d => x = d / 3.

   Show worked solution

   Step 1: Balance forces: G·m·M / x² = G·(4m)·M / (d - x)². Step 2: 1 / x² = 4 / (d - x)² => 1 / x = 2 / (d - x). Step 3: d - x = 2x => 3x = d => x = d / 3. Answer: d / 3.
   Modelled on: the A/L Physics examination pattern

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Where does Newton’s Law of Gravitation fit in the syllabus?

Unit 5.1 · Year 1 · Term 3