General Science Previous Year Questions (PYQ) with Answers – Page 67

With constant acceleration the distance covered is s = ut + ½at², and the first term contains the initial velocity u. This is the second equation of motion.

Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.

Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.

Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.

Propane is a light gaseous hydrocarbon that burns completely with a blue flame, leaving no smoke, soot or ash. A clean fuel burns completely, gives high heat and releases few pollutants.

Soft soaps are potassium salts of fatty acids, while ordinary hard bar soaps are sodium salts. Soap is made by saponification, heating an oil or fat with an alkali.

This is sodium stearate, the sodium salt of a long-chain fatty acid, which makes it a soap and not a synthetic detergent.

This statement is false: water is a strongly polar molecule. In a water molecule the oxygen atom is much more electronegative than hydrogen, so it pulls the shared electrons towards itself and carries a partial negative charge, while the two hydrogens carry partial positive charges.

Power equals force times velocity, so the force is 3,000 W divided by 5 m/s, which is 600 N. Power is the rate of doing work: P = W/t. Work is force times distance, W = F × d, so P = F × d/t, and since d/t is the…

A wave carries energy from one place to another, while the particles of the medium only vibrate about their fixed positions.

Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.

Portland cement is made by heating a mix of limestone, which supplies lime, with clay, which supplies silica and alumina.

The apple's gravitational potential energy first becomes kinetic energy as it falls, some is lost as heat to the air on the way, and at impact the rest goes into heating the ground and apple and into sound.

Diamond and graphite are allotropes of the same element, carbon, so their chemical properties are the same; only their physical properties differ.

A satellite is given the required height and speed by its launch vehicle, and after that no engine is needed: the gravitational pull of the earth alone acts on it and provides the centripetal force that keeps it in a curved path, so the satellite keeps falling towards the earth…

In boiling, bubbles of vapour form throughout the liquid; in evaporation, only molecules at the surface escape.

Chemical energy is the energy stored in the bonds that link atoms together in molecules. When a chemical reaction breaks old bonds and forms new ones, this stored energy is released or absorbed.

This statement is wrong: soda glass is the soft glass, while pyrex is a hard borosilicate glass. Ordinary soda-lime glass is made from silica (sand), sodium carbonate and limestone; it softens at a fairly low temperature and is used for windows, bottles and tumblers.

When the two mix, they release a rush of carbon dioxide that pushes water out onto the fire. In a soda-acid extinguisher a small bottle of dilute sulphuric acid sits inside a cylinder filled with a solution of sodium hydrogencarbonate (baking soda, NaHCO3).

Vitamin C has no carboxyl group; its acidity comes from an enol group in its ring. Ascorbic acid, C6H8O6, is a five-membered lactone ring carrying hydroxyl groups.