Fundamental laws of physics require
- A.conservation of energy and non-conservation of charge.
- B.conservation of charge and non-conservation of linear momentum.
- C.conservation of charge and non-conservation of energy.
- D.conservation of energy, momentum and charge.
Correct answer
Explanation
The correct answer is D, conservation of energy, momentum and charge. In every isolated system these three quantities stay constant, and no known process has ever been found to break these laws.
The law of conservation of energy says energy can change form, from chemical to heat or from kinetic to potential, but its total stays the same. Conservation of linear momentum follows from Newton's third law: in a collision or explosion with no outside force, the total momentum before equals the total after, which is why a gun recoils. Conservation of charge says electric charge can only be transferred, never created or destroyed; when a glass rod is rubbed with silk, the charges on the two are equal and opposite.
A is wrong because charge is always conserved. B is wrong because linear momentum is conserved when no external force acts. C is wrong because energy is always conserved; it only changes form.
Exam tip: energy, linear momentum, angular momentum and charge are all conserved in an isolated system.
Practice Questions
View allWhich one of the following is monatomic?
- A.Hydrogen
- B.Sulphur
- C.Phosphorus
- D.Helium
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A monatomic element exists as single, separate atoms. Helium is a noble gas of group 18: its only shell, the first, is full with two electrons, so a helium atom has no tendency to share or transfer electrons and does not bond even with another helium atom.
Read the full explanation →The normal systolic pressure in human beings is :
- A.80 mm of Hg
- B.100 mm of Hg
- C.120 mm of Hg
- D.140 mm of Hg
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Blood pressure is written as two numbers, and normal adult blood pressure is about 120/80 mm of mercury.
Read the full explanation →'Study of human societies and cultures from the oldest times to the present' is the work of
- A.Archaeologists
- B.Anthropologists
- C.Palaeontologists
- D.Geologists
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Anthropology, from the Greek 'anthropos' (human) and 'logos' (study), is the science of human beings: how societies and cultures began, how they changed and how people live today.
Read the full explanation →Which of the following catalytic systems is used for the reduction of unsaturated hydrocarbon to saturated hydrocarbon?
- A.Copper and H2
- B.Iron and H2
- C.Zinc and H2
- D.Nickel and H2
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Adding hydrogen across the double or triple bond of an alkene or alkyne turns it into a saturated alkane; this reaction is called hydrogenation and it needs a catalyst.
Read the full explanation →Which one among the following is not a plant hormone ?
- A.Gibberellins
- B.Abscisic acid
- C.Auxins
- D.Thyroxine
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Thyroxine is an animal hormone, made by the thyroid gland in the neck, and it controls the rate of metabolism in the human body.
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