Which one among the following statements is correct?
- A.The total mechanical energy of a system is conserved if the forces, doing work on it, are conservative.
- B.The total mechanical energy of a system is conserved if the forces, doing work on it, are non-conservative.
- C.The total mechanical energy of a system remains constant.
- D.Every force encountered in mechanics does have an associated well-defined potential energy.
Correct answer
Explanation
The correct answer is A. When only conservative forces do work on a system, the sum of its kinetic and potential energy stays the same; this is the principle of conservation of mechanical energy.
A force is conservative when the work it does depends only on the start and end points, not on the path, so the work done round a closed path is zero. Gravity, the spring force and the electrostatic force are examples, and each has a potential energy defined for it. When a ball falls freely, its potential energy turns into kinetic energy, but the total stays constant. Friction and air drag are non-conservative: they turn mechanical energy into heat and sound, so mechanical energy falls even though total energy is still conserved.
B is wrong because non-conservative forces such as friction drain mechanical energy. C is wrong because mechanical energy stays constant only when non-conservative forces do no work. D is wrong because forces like friction have no potential energy associated with them.
Exam tip: conservative force → path-independent work → potential energy exists → KE + PE constant.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- 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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Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- 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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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- 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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They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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