Which one of the following statements for second law of motion is NOT correct?
- A.The net force on a body is proportional to that body's acceleration
- B.The net force on a body is in the same direction as the acceleration
- C.The time rate of change of momentum is equal to force
- D.The net force on a body is proportional to that body's momentum
Correct answer
Explanation
The correct answer is D, The net force on a body is proportional to that body's momentum. Force depends on how fast momentum changes, not on the momentum itself.
Newton's second law states that the rate of change of momentum of a body is proportional to the net force on it and takes place in the direction of the force. With suitable units F = dp/dt, and for constant mass this becomes F = ma. A body moving at high, steady velocity has large momentum but zero net force on it, which shows that force is not proportional to momentum.
A is wrong: this statement is correct, because for a given mass F = ma, so force is proportional to acceleration.
B is wrong: this statement is correct, because acceleration always points along the net force.
C is wrong: this statement is correct; it is the exact form of the second law, F = dp/dt.
Exam tip: first law defines inertia, second law gives F = ma = dp/dt, third law gives equal and opposite action and reaction.
Practice Questions
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- A.haploid zygote
- B.diploid zygote
- C.non-motile male gametes
- D.motile male gametes
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Syngamy is the fusion of a male and a female gamete, and since each gamete is haploid, their union gives a diploid zygote.
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- A.One
- B.Two
- C.Three
- D.Four
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- A.10⁻⁷ cm
- B.10⁻⁶ cm
- C.10⁻⁴ cm
- D.10⁻³ cm
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Read the full explanation →Which of the following is the general formula for saturated hydrocarbons?
- A.CₙH₂ₙ₊₂
- B.CₙH₂ₙ₋₂
- C.CₙH₂ₙ₊₁
- D.CₙH₂ₙ₋₁
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- A.Cholera
- B.Malaria
- C.Smallpox
- D.Elephantiasis
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Elephantiasis, or lymphatic filariasis, is an endemic disease: it stays steadily present in certain regions and develops slowly over years, rather than breaking out suddenly in a large number of people.
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