General Science Mixed Quiz: Set 49

The correct answer is A, 35 m. First find the throwing speed from the height: v squared equals u squared minus 2 g h gives u equal to the square root of 2 into 10 into 80, that is 40 metres per second. The ball therefore takes 4 seconds to reach the top, since 40 divided by 10 is 4. Three seconds of the 7 are left for the fall, and in them the ball drops half of 10 into 9, that is 45 metres. Its height above the start is 80 minus 45, which is 35 metres. B is wrong because 125 metres is the total distance covered, 80 up plus 45 down, not the displacement. C is wrong because 45 metres is only the fall in the last 3 seconds. D is wrong because 25 metres matches no step of the working. Exam tip: time up equals time down, so for a ball reaching 80 metres the flight lasts 8 seconds in all.

The correct answer is C, Thallophyta. Litmus is a purple dye taken from lichens, and in the classification used in school science lichens are placed in Thallophyta, the group of simple plants whose body is an undifferentiated thallus with no true root, stem or leaf. Algae and fungi belong to the same group, and a lichen is in fact a partnership of an alga and a fungus living together. Litmus is a natural indicator: it stays purple in a neutral solution, turns red in acid and blue in base, and is used both as a solution and as litmus paper. Option A is wrong because gymnosperms are well developed plants with naked seeds, such as pine and cycas. Option B is wrong because pteridophytes, the ferns, are the first plants with vascular tissue. Option D is wrong because bryophytes such as moss and Marchantia are called the amphibians of the plant kingdom. Exam tip: litmus is red in acid, blue in base and purple when neutral.

The correct answer is B, 50J. By the work-energy theorem the work done by a force equals the change in kinetic energy, so the work here is half of 4 kilograms times 5 metres per second squared, that is 0.5 into 4 into 25, which gives 50 joules. The body starts from rest, so its initial kinetic energy is zero and the whole of the final kinetic energy has come from the force. Notice that neither the size of the force nor the distance moved is needed; the theorem settles the answer from the masses and speeds alone, which is why it is the quickest route in the exam hall. A is wrong because 40 joules would follow from using the speed once instead of squaring it. C is wrong because 30 joules matches no step of the calculation. D is wrong because 60 joules would need a mass of 4.8 kilograms at the same speed. Exam tip: work equals change in kinetic energy, half m v squared.

The correct answer is C. Ultraviolet light is a transverse wave, not a longitudinal one, so this statement is the wrong one. In an electromagnetic wave the electric and magnetic fields vibrate at right angles to each other and to the direction the wave travels, which is the definition of a transverse wave. Longitudinal waves need a material to squeeze and stretch, and sound is the standard example. Option A is correct because ultraviolet light sits in the electromagnetic spectrum between visible light and X-rays. Option B is correct because electromagnetic waves need no medium and cross empty space, which is how the Sun's ultraviolet rays reach the earth. Option D is correct because ultraviolet wavelengths run from about 400 nanometres down to 10 nanometres, shorter than violet light, and this higher energy is what burns skin and is absorbed by the ozone layer. Exam tip: all electromagnetic waves are transverse; only mechanical waves such as sound can be longitudinal.

The correct answer is A, Diminished. A concave lens, also called a diverging lens, spreads out the rays that fall on it and so can never bring them to a real focus. Wherever the object stands, anywhere from infinity up to the optical centre, the image is always virtual, erect, smaller than the object, and formed on the same side as the object, between the focus and the optical centre. That is why a concave lens corrects myopia, or short-sightedness: it shrinks and shifts the image so that a near-sighted eye can bring it to the retina. Option B is wrong because a point-size image appears only in the special case of an object exactly at infinity, not over this whole range. Option C is wrong because an image of the same size needs a convex lens with the object at twice the focal length. Option D is wrong because a diverging lens never magnifies. Exam tip: a concave lens always gives a virtual, erect and diminished image.

The correct answer is C, Avogadro. The statement in the question is Avogadro's law, given by the Italian scientist Amedeo Avogadro in 1811. It says that equal volumes of all gases at the same temperature and pressure hold the same number of molecules, so the volume of a gas is directly proportional to the number of moles in it. This is why one mole of any gas occupies 22.4 litres at standard temperature and pressure, and why the number of particles in one mole, about 6.022 x 10 to the power 23, is named the Avogadro number after him. A is wrong because Charles law links the volume of a fixed mass of gas to its temperature at constant pressure. B is wrong because Boyle's law says that volume varies inversely with pressure at constant temperature. D is wrong because Gay-Lussac gave the law of combining volumes and the pressure-temperature law. Exam tip: Avogadro ties volume to the number of molecules, Boyle to pressure and Charles to temperature.

The correct answer is A, 0.36 A. Reduce the parallel pair first: 20 into 30 divided by 50 gives 12 ohms. Adding the 8 ohm resistor in series makes the circuit resistance 20 ohms, so the battery drives 12 volts divided by 20 ohms, that is 0.6 ampere, through the whole circuit. That current passes through the 12 ohm combination and drops 0.6 into 12, which is 7.2 volts across it. Both parallel branches share this same 7.2 volts, so the 20 ohm branch carries 7.2 divided by 20, which is 0.36 ampere. B is wrong because 0.12 ampere matches no branch of this circuit. C is wrong because 0.24 ampere is the current in the 30 ohm branch, and the two branch currents add up to 0.6. D is wrong because 0.60 ampere is the total current from the battery, not the share of the 20 ohm resistor. Exam tip: in parallel the voltage is common and the current splits in the inverse ratio of the resistances.

The correct answer is C, Stomata. Stomata are the tiny pores on the surface of a leaf through which a plant takes in carbon dioxide and gives out oxygen and water vapour, so the exchange of gases takes place through them. Each stoma is bounded by two bean-shaped guard cells that swell to open the pore and shrink to close it, and this is how the plant controls its water loss. Most stomata lie on the lower surface of a leaf, so less water is lost to direct sunlight. Transpiration also happens largely through these pores. A is wrong because the cell membrane controls what enters and leaves a single cell, not the gas exchange of the whole plant. B is wrong because the nucleus carries the genetic material and directs the activities of the cell. D is wrong because guard cells only open and close the pore, while the exchange itself happens through the stomatal opening. Exam tip: stomata do the gas exchange and transpiration, guard cells only open and close them.

The correct answer is A, F. Fluorine is the most electronegative element, so in every compound it pulls the shared electrons towards itself and always shows an oxidation number of -1.

Because no element is more electronegative than fluorine, nothing can take electrons away from it, so it never shows a positive oxidation state. In the free state, as the molecule F2, its oxidation number is zero, which is true of every element in its elemental form, but in a compound the value is fixed at -1. The other halogens are less electronegative, so they can take positive values when they are bonded to fluorine or to oxygen.

B is wrong: chlorine shows +1, +3, +5 and +7 in compounds such as HClO and HClO4. C is wrong: bromine likewise shows +1 and +5, as in HBrO3. D is wrong: iodine shows +1, +5 and +7, as in HIO3.

Exam tip: fluorine is the most electronegative element, so its oxidation number in any compound is always -1.

The correct answer is B, In the same direction. In a class 3 lever the fulcrum is at one end, the effort is applied in the middle and the load sits at the far end. Since both the effort and the load lie on the same side of the fulcrum, the beam turns one way and they move in the same direction. The effort arm is shorter than the load arm, so the mechanical advantage is less than one and more effort is needed than the load; what such a lever gains is speed and a wider sweep of movement. The human forearm, a pair of sugar tongs, a fishing rod and a stapler work this way. A is wrong because effort and load move oppositely in a class 1 lever, where the fulcrum lies between them, as in a see-saw or scissors. C is wrong because a lever turns about a fixed point and its two ends never move at right angles to each other. D is wrong because the size of the load changes the force needed, not the direction of motion. Exam tip: class 1 has the fulcrum in the middle, class 2 the load, class 3 the effort.

The correct answer is B, the thyroid gland, a butterfly-shaped gland in front of the windpipe in the neck, which is the largest purely endocrine gland in the body and secretes thyroxine, triiodothyronine and calcitonin. Option A is wrong because the pituitary is the smallest endocrine gland, about the size of a pea, although it is the master gland that controls several others, so the two make a standard pair of opposites in exams. Option C is wrong because the adrenal glands, one above each kidney, are small, and they are remembered for adrenaline rather than for size. Option D is wrong on a technicality worth knowing: the pancreas is larger than the thyroid, but it is a mixed or heterocrine gland, part exocrine for digestive juice and part endocrine for insulin, so the largest purely endocrine gland remains the thyroid.

The correct answer is A, Papaya. A unisexual flower carries only one kind of reproductive organ, either stamens or a pistil, while a bisexual flower carries both. Papaya is dioecious: male and female flowers are borne on separate plants, so pollen must travel from a male tree to a female tree before fruit can set, which is why growers keep a few male trees in a papaya orchard. Other familiar unisexual examples are maize, cucumber, watermelon and coconut, in which the two kinds of flower sit on the same plant and the plant is called monoecious. Option B is wrong because the disc florets of a sunflower head are bisexual. Option C is wrong because the hibiscus flower is a standard bisexual flower carrying both stamens and a pistil. Option D is wrong because mustard, a member of the family Brassicaceae, also bears bisexual flowers. Exam tip: unisexual flowers include papaya, maize, cucumber and watermelon, while hibiscus, mustard, rose and pea are bisexual.

The correct answer is C, vitamin C. Vitamin C, chemically ascorbic acid, is needed to make collagen, the protein that holds tissues together; without it the gums swell and bleed, wounds refuse to heal and the joints ache, and the disease is called scurvy. Amla, guava, citrus fruit and tomato are rich sources, and the vitamin is destroyed by heat. Option A is wrong because a shortage of vitamin A gives night blindness and xerophthalmia, disorders of the eye. Option B is wrong because a shortage of vitamin B12 gives pernicious anaemia, a disorder of the blood. Option D is wrong because a shortage of vitamin K delays the clotting of blood, since prothrombin cannot be made in the liver without it. Scurvy was the classic disease of long sea voyages before fresh fruit was carried.

The correct answer is B, Static friction > Kinetic friction > Rolling friction. For the same pair of surfaces the order of friction is always static, then kinetic, then rolling. Static friction is the largest because the surfaces interlock while at rest and that grip has to be broken to start motion. Once sliding begins the contact keeps breaking and remaking, so kinetic friction is smaller. Rolling friction is the smallest of the three, since a rolling wheel does not slide over the road but only presses and deforms it slightly at the point of contact. This is exactly why wheels, rollers and ball bearings are used to shift heavy loads. A and D are wrong because they place rolling friction at the top, though it is the least of the three. C is wrong because it puts rolling friction above kinetic friction, reversing the true order. Exam tip: static greater than kinetic greater than rolling; the smallest of them gave us the wheel.

The correct answer is C, oxygen. Photosynthesis makes carbohydrate and gives out oxygen, and of the four choices here only oxygen is something the plant produces.

A green plant uses sunlight trapped by chlorophyll to turn carbon dioxide and water into sugar, and the equation is 6CO2 plus 6H2O giving C6H12O6 plus 6O2. The oxygen comes from the splitting of water in the light reaction, not from carbon dioxide, as experiments with heavy oxygen showed. The glucose made in the dark reaction is stored as starch, and the oxygen escapes through the stomata. This is the source of almost all the oxygen in the air we breathe.

A is wrong: plants do not make hydrocarbons in photosynthesis. B is wrong: carbon dioxide is a raw material taken in, not a product. D is wrong: water too is a raw material and is used up when it is split.

Exam tip: photosynthesis takes in carbon dioxide and water and gives out glucose and oxygen, and the oxygen comes from water.

The correct answer is C, 2 s. A simple pendulum about one metre long completes one full swing in roughly two seconds, and a pendulum of this length is called the seconds pendulum. The time period of a simple pendulum is T = 2 pi times the square root of L divided by g, where L is the length of the thread and g is the acceleration due to gravity, about 9.8 metres per second squared. Putting L = 1 metre gives T = 2 x 3.14 x the square root of 1 divided by 9.8, which comes to about 2.01 seconds. The period depends only on the length and on g, not on the mass of the bob or on how far it is pulled aside, so long as the swing is small. A is wrong because a 6 second period needs a thread about 9 metres long. B is wrong because a 4 second period needs a thread about 4 metres long. D is wrong because a 1 second period belongs to a thread of only about 25 centimetres. Exam tip: the period doubles only when the length becomes four times.

The correct answer is C, mRNA copy. Protein synthesis begins with transcription, in which the message of a gene is copied from DNA into messenger RNA, so the first event is the making of an mRNA copy. The mRNA leaves the nucleus, reaches a ribosome in the cytoplasm and is read three bases at a time; each triplet, called a codon, calls for one amino acid, which transfer RNA brings to the ribosome. This second stage is translation, and the chain of amino acids folds into the protein. A is wrong because copying DNA into DNA is replication, which happens before cell division and not during protein synthesis. B is wrong because it is too loose: transfer RNA and ribosomal RNA are also RNA, but the copy that carries the gene's message is mRNA. D is wrong because no DNA copy is made here at all. Exam tip: DNA to RNA is transcription, RNA to protein is translation, DNA to DNA is replication.

The correct answer is D, Oil in water. Oil does not dissolve in water; it stays as a separate layer or as floating droplets, so the mixture is heterogeneous and the boundary between the two liquids can be seen. A homogeneous mixture has the same composition throughout and its parts cannot be told apart even under a microscope, which is what happens when a solid dissolves in water to give a true solution. Oil and water part because water is a polar liquid while oil is non-polar, and like dissolves like; shaking them with a soap gives an emulsion, which is still not homogeneous. A is wrong because copper sulphate dissolves to give a clear blue solution of one phase. B is wrong because sugar in water is the classic true solution. C is wrong because common salt dissolves completely into sodium and chloride ions. Exam tip: a true solution is homogeneous, while a suspension and an emulsion such as oil in water or milk are heterogeneous.

The correct answer is D, Cohesion. Wetting is decided by a contest between two forces: cohesion, the attraction among the molecules of the liquid itself, and adhesion, the attraction between the liquid and the solid surface. In mercury the cohesive force between its own atoms is far stronger than its adhesion to glass, so the metal pulls itself into rounded drops and refuses to spread. Water behaves the other way round, its adhesion to glass beating its cohesion, so it spreads and wets the surface. The same rule explains the meniscus: mercury in a glass tube curves upward in a convex dome and has an angle of contact above 90 degrees, while water dips in a concave curve. Option A is wrong because viscosity measures how a fluid resists flow, not whether it clings to a solid. Option B is wrong because surface tension arises out of cohesion but is not the comparison being asked for. Option C is wrong because adhesion is the weaker force here, not the reason. Exam tip: cohesion stronger than adhesion means no wetting and a convex meniscus.

The correct answer is C, Cu + Sn. Bronze is an alloy of copper and tin, usually about 88 per cent copper to 12 per cent tin. Tin makes copper harder and gives it a far better resistance to rust and sea water, which is why bronze is used for statues, temple bells, coins, medals and ship fittings. It was the first alloy people made in quantity and the Bronze Age takes its name from it; the Dancing Girl of Mohenjo-daro is a bronze casting. A is wrong because aluminium with copper, manganese and magnesium is duralumin, a light alloy used in aircraft. B is wrong because copper with zinc is brass, the yellow alloy of utensils and musical instruments. D is wrong because lead with tin is solder, the low-melting alloy used to join wires. Exam tip: fix the three copper alloys - bronze is copper and tin, brass is copper and zinc, German silver is copper, zinc and nickel.