Which one of the following forces is non-central and non-conservative ?
- A.Frictional force
- B.Electric force
- C.Gravitational force
- D.Mechanical force
Correct answer
Explanation
The correct answer is A, Frictional force. Friction acts along the surfaces in contact, opposite to the direction of motion, not along the line joining the centres of two bodies, so it is non-central. It is also non-conservative: the work done against friction depends on the path taken, and over a closed path it is not zero, because the energy is lost as heat. A conservative force is one whose work depends only on the starting and end points, so a potential energy can be defined for it. A central force always acts along the line joining the two interacting bodies. Option B is wrong because the electrostatic force between two charges acts along the line joining them and its work is path-independent, so it is both central and conservative. Option C is wrong because gravity between two masses is likewise central and conservative, which is why we speak of gravitational potential energy. Option D is wrong because 'mechanical force' is a general term, not a specific force with these fixed properties. Exam tip: gravity and electrostatic force are central and conservative; friction and air drag are non-conservative.
Practice Questions
View allChlorophyll in photosynthetic prokaryotic bacteria is associated with
- A.plastids
- B.membranous vesicles
- C.nucleoids
- D.chromosomes
Show answer
Photosynthetic bacteria have no chloroplasts; their pigments sit on infoldings of the cell membrane that form vesicles or sacs, often called chromatophores.
Read the full explanation →Fat in human body is stored in
- A.Adipose tissue
- B.Red blood cells
- C.Muscle tissue
- D.Epithelial tissue
Show answer
Adipose tissue is a loose connective tissue whose cells, called adipocytes, are built to store fat. Each cell holds a large droplet of fat that pushes the nucleus and cytoplasm to one side.
Read the full explanation →Which one of the following is a metalloid ?
- A.Germanium
- B.Coke
- C.Iodine
- D.Sugar
Show answer
Germanium is a metalloid, an element whose properties lie between those of metals and non-metals. It is a hard, shiny, grey-white solid like a metal, yet it is brittle and conducts electricity far less well than a metal, which makes it a semiconductor.
Read the full explanation →A photon of X-ray has energy of 1 keV. A photon of visible radiation has energy of 3 eV. In this context, which one of the following statements is not correct?
- A.The wavelength of X-ray photon is less than the wavelength of visible radiation photon.
- B.Both the photons have different energies.
- C.The speeds of both the photons in vacuum are different.
- D.The frequency of X-ray photon is higher than the frequency of visible radiation photon.
Show answer
This statement is wrong because every photon, whatever its energy, travels in vacuum at the same speed of light, about 3 × 10^8 metres per second.
Read the full explanation →Which of the following substances cause temporary hardness in water?
1. Mg(HCO3)2
2. Ca(HCO3)2
3. CaCl2
4. MgSO4
Select the correct answer using the code given below.
- A.3 and 4
- B.2 and 3
- C.1 and 4
- D.1 and 2
Show answer
Temporary hardness is caused by the bicarbonates of magnesium and calcium, Mg(HCO3)2 and Ca(HCO3)2. It is called temporary because simple boiling removes it: on heating, the soluble bicarbonates break down into insoluble carbonate or hydroxide, carbon dioxide and water, and the solid settles out.
Read the full explanation →