What is the value of the gravitational constant G?

Correct answer: c 6.67 × 10⁻¹¹ Nm² kg⁻²

G = 6.67 × 10⁻¹¹ Nm²kg⁻²; this unit follows from F = Gm₁m₂/r².

Why the other options are wrong

• a 6.67 × 10¹¹ Nm² kg⁻²: The sign of the exponent is wrong; G is extremely small, so the exponent is negative (10⁻¹¹).
• b 6.67 × 10⁻¹¹ Nm⁻² kg⁻²: The number is right but the unit Nm⁻² is wrong; from F = Gm₁m₂/r² the unit of G is Nm²kg⁻².
• d 6.67 × 10¹¹ Nm² kg⁻¹: Both the exponent and kg⁻¹ are wrong; the unit of G is Nm²kg⁻².