The universal constant of gravitation G has the unit
- A.N
- B.m/s
- C.Joule
- D.N-m²/kg²
Correct answer
Explanation
The correct answer is D, N m²/kg². Rearranging Newton's law of gravitation gives G = F r² / (m₁ m₂), so its unit is newton × metre² ÷ kilogram².
Newton's law says that the force between two masses is F = G m₁ m₂ / r². Putting the SI units into G = F r² / (m₁ m₂) gives N m² kg⁻². The value of G is about 6.67 × 10⁻¹¹ N m²/kg², first measured in the laboratory by Henry Cavendish in 1798 with a torsion balance. G is a universal constant: it is the same everywhere, unlike g, the acceleration due to gravity, which changes with height, depth and latitude.
A is wrong because the newton is the unit of force, which is F itself, not G. B is wrong because m/s is the unit of speed or velocity. C is wrong because the joule is the unit of work and energy.
Exam tip: G = 6.67 × 10⁻¹¹ N m²/kg² (constant everywhere); g = 9.8 m/s² (varies from place to place).
Practice Questions
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- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
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