Two bodies of masses 3.0 kg and 2.0 kg are separated by a distance of 50 cm. Calculate the force of attraction…

Analyze the question: We need the gravitational force between two masses using Newton's law of universal gravitation.

Concept: F = G·m₁·m₂ / r²

Remember to convert the distance to metres: 50 cm = 0.50 m.

Solution:

F = (6.67 × 10⁻¹¹ × 3.0 × 2.0) / (0.50)²

• Numerator: 6.67 × 10⁻¹¹ × 6.0 = 40.02 × 10⁻¹¹ = 4.002 × 10⁻¹⁰
• Denominator: 0.25

F = 4.002 × 10⁻¹⁰ / 0.25 = 16.008 × 10⁻¹⁰ ≈ 1.6 × 10⁻⁹ N

Answer: The force is about 1.6 × 10⁻⁹ N, which matches option A.

Options B, C and D are huge values (thousands of newtons). Gravitational forces between small everyday masses are always extremely tiny, so you can eliminate them immediately.

Tip: Always convert cm to m before substituting. If you forgot and used 50 instead of 0.5, you would get a wrong value. Also, G is very small (10⁻¹¹), so for small masses the answer must be a very small number.