General Science GK Questions with Answers – Page 33

In mitosis each centromere splits in anaphase and one chromatid of every chromosome goes to each pole, so the two daughter cells receive exactly the same number of chromosomes as the parent cell had, and exactly the same genetic information.

During this phase the DNA of the cell is copied so that the amount of DNA in the nucleus doubles, while the number of chromosomes remains unchanged because each chromosome now simply consists of two identical sister chromatids joined at the centromere.

In uniform circular motion the magnitude of the velocity does not change, so the acceleration can have no component along the direction of motion; the whole of it is perpendicular to the velocity and points to the centre, which is why it is called centripetal, meaning centre seeking, and its…

To move along a curve a body needs a force directed towards the centre of that curve.

A shaft turning directly inside a sleeve slides against it, and sliding friction is large; placing hard steel balls between the shaft and its housing makes the surfaces roll over one another instead, and rolling friction is a small fraction of sliding friction, so less energy is wasted and the…

On a banked road the normal reaction is tilted, its vertical component balances the weight and its horizontal component supplies the centripetal force; dividing one equation by the other leaves the tangent of the banking angle equal to the square of the speed divided by the radius multiplied by the…

The angle of repose is the angle to which an inclined plane must be tilted before a body resting on it just begins to slide.

Distance is the length of the actual path and displacement is the straight line from the start to the finish, so on a curved path the two can never be equal: the arc of a circle is always longer than the chord joining its ends.

The centrifugal force has the same magnitude as the centripetal force, which for a body moving in a circle is the mass multiplied by the square of the angular velocity multiplied by the radius.

In uniform circular motion the body covers equal arcs in equal times, so its speed, a scalar, does not change; its kinetic energy and its angular velocity are constant too.

When a body rolls, the surfaces in contact change continuously and the irregularities have no time to interlock deeply, so rolling friction is very much smaller than sliding friction; this single fact is the reason the wheel was invented and the reason a ball bearing is fitted wherever a shaft…

The coefficient of friction is the ratio of the limiting or kinetic frictional force to the normal reaction, and since both are forces the ratio is a pure number; the same reasoning applies to other ratios such as the refractive index and relative density.

Friction is defined as the force that opposes the relative motion, or the tendency of relative motion, between two surfaces in contact; it acts along the surfaces and always against the direction of motion.

Only statement 3 is correct: the acid must be added slowly to water, and dilution lowers the concentration of hydronium ions per unit volume.

Planck's constant has the same dimensions as angular momentum, [M L² T⁻¹].

Biogas is mainly methane and carbon dioxide. Biogas is produced when bacteria break down animal dung, crop waste and kitchen waste in the absence of oxygen, a process called anaerobic digestion.

A soda-acid extinguisher uses sodium hydrogen carbonate (baking soda) solution and sulphuric acid, which react to release carbon dioxide. In this extinguisher the sulphuric acid is kept in a separate container inside a cylinder filled with sodium hydrogen carbonate solution.

Nerve impulses are carried by the movement of sodium and potassium ions across the membrane of the nerve cell, so sodium is essential.

Salmonella typhi is a rod-shaped bacterium that causes typhoid fever in human beings. Typhoid spreads through food and water contaminated with the faeces of an infected person.

Magnetic field lines are always closed curves, so the statement that they are open curves is the incorrect one. Outside a magnet, field lines run from the north pole to the south pole; inside the magnet they continue from the south pole back to the north pole, closing the loop.