Which one among the following statements is not correct?
- A.All bodies in the universe attract each other due to the gravitational force.
- B.Newton's law of gravitation follows from Newton's laws of motion.
- C.The value of g (acceleration due to gravity) at the centre of the Earth is zero.
- D.Mass and weight are measured in different units.
Correct answer
Explanation
The correct answer is B. Newton's law of gravitation is an independent law of nature; it cannot be derived from his three laws of motion.
The laws of motion tell how a body moves when a force acts on it, but they say nothing about what that force is or how strong it is. The law of gravitation adds something new: every two masses attract each other with a force F = Gm₁m₂/r², proportional to the product of the masses and inversely proportional to the square of the distance. Newton used the law of gravitation together with the laws of motion to explain the orbits of the planets, but the two are separate statements.
A is correct, because gravitation is universal and acts between every pair of bodies.
C is correct, because g = g₀(1 − d/R) inside the Earth, which becomes zero at the centre where d = R.
D is correct, because mass is measured in kilograms and weight, being a force, in newtons.
Exam tip: g falls both on going up and on going down; it is zero at the centre and greatest at the surface.
Practice Questions
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- C.Lysosome
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- C.Potato, onion, garlic
- D.Potato, garlic, turnip
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- B.1 s
- C.1.5 s
- D.2 s
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- A.equal to its weight.
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- C.greater than its weight.
- D.zero.
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Show answer
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