General Science Previous Year Questions (PYQ) with Answers – Page 86

The ball falls from 10 m but rises back only 2.5 m, so it keeps one quarter of its energy and loses three quarters.

Argon is a noble gas whose outer shell already holds eight electrons, so it has no room to take another one easily; adding an electron would mean starting a new shell, and energy has to be supplied rather than released.

At the top the object holds only potential energy; as it falls, that store is steadily converted into kinetic energy, and just as it touches the ground almost all of it is kinetic.

Fibrous roots are the mark of monocotyledonous plants such as wheat, maize, rice and grasses, not of dicots.

The work done in moving a charge across a potential difference is W = QV, so W = 5 × 16 = 80 joules.

A healthy human ear can hear sound waves with frequencies from about 20 hertz to 20,000 hertz (20 kHz); this band is called the audible range.

The nucleus is called the master or control centre of the cell because it directs all the activities of the cell.

Brass is an alloy of copper and zinc, usually about 70 per cent copper and 30 per cent zinc. Adding zinc makes brass harder than pure copper, gives it a golden-yellow shine and helps it resist corrosion.

Bleaching powder gives off chlorine when it reacts with water, and this chlorine does the bleaching and kills germs. Bleaching powder is calcium oxychloride, CaOCl2, made by passing chlorine gas over dry slaked lime, Ca(OH)2.

Carbon dioxide reacts with lime water to form calcium carbonate, which does not dissolve, and its fine white particles make the water look milky.

Vitamin K is needed to make the clotting proteins, so without it even a small cut keeps bleeding. The liver uses vitamin K to make prothrombin and other clotting factors that turn blood into a clot at a wound.

The medulla oblongata is the breathing centre of the brain, which is why we keep breathing even while asleep. It is the lowest part of the hindbrain and joins the brain to the spinal cord.

The d-block occupies the middle of the modern periodic table, groups 3 to 12, and its members are also called transition elements.

A red blood cell is a biconcave disc, thin in the middle and thick at the edge, not an amoeboid cell.

In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.

Tincture of iodine is made from iodine, potassium iodide, alcohol and water; acetone is not one of its ingredients. A tincture is a solution in alcohol.

Natural rubber is a polymer of isoprene, a hydrocarbon, and contains no sugar units at all. Natural rubber is cis-1,4-polyisoprene, obtained from the latex of the rubber tree Hevea brasiliensis; its monomer isoprene (2-methyl-1,3-butadiene) has the formula C5H8.

Only a pressure greater than the osmotic pressure of seawater can push pure water backwards through the membrane. In ordinary osmosis, water moves through a semipermeable membrane from the dilute side to the concentrated side.

Bacteria on the floor break down the urea in urine and release ammonia, which has a sharp, pungent smell. Urea, CO(NH2)2, is the main nitrogenous waste of humans.

With no net force acting on it, the object keeps moving at the same speed in the same straight line.