General Science Mixed Quiz: Set 15

The correct answer is C, zero. Constant velocity means no acceleration, and by Newton's second law force equals mass into acceleration, so the net force must be zero.

Newton's first law says a body continues in its state of rest or of uniform motion in a straight line unless an external force acts on it, which is why motion at a steady speed in a fixed direction needs no force to keep it going. Force is needed only to change the speed or the direction. A car moving at a steady 60 km per hour on a straight road is in the same state: the engine's push only balances friction and air resistance, so the forces cancel and the net force is zero. Such a body is said to be in equilibrium.

Options A, B and D are wrong because any net force in a direction would produce acceleration and so change the velocity, which contradicts the given condition of constant velocity.

Exam tip: constant velocity means zero acceleration and therefore zero net force, not zero force at all.

The correct answer is A, Liquid. At normal atmospheric pressure water stays liquid between 0 °C and 100 °C, and 12 °C lies inside that range. Water freezes into ice at 0 °C, which is its melting point, and boils into steam at 100 °C, which is its boiling point, when the pressure is one atmosphere. Between these two fixed points the molecules have enough energy to slide over one another but not enough to fly apart, so water flows and takes the shape of its container while keeping a fixed volume. Water does evaporate slowly at 12 °C from an open surface, but that happens only at the top layer and does not change the state of the water below. Option B is wrong because ionic is not a state of matter at all; it describes a kind of bond or compound. Option C is wrong because water becomes a gas, that is steam, only above 100 °C. Option D is wrong because water turns solid only at or below 0 °C. Exam tip: remember 0 °C and 100 °C as the fixed points of water at one atmosphere.

The correct answer is B, 0 J. The body is thrown up at 20 m/s and gravity takes away 10 m/s of speed every second, so after 2 seconds its speed is zero. Using v = u − gt, we get v = 20 − 10 × 2 = 0 m/s. Kinetic energy is half m v squared, and with v = 0 the kinetic energy is also zero. At that instant the body is at the highest point of its path and all of its energy is potential energy, mgh = 2 × 10 × 20 = 400 J, since the body has risen 20 m. A moment later it begins to fall and the kinetic energy grows again. Option A is wrong because 100 J needs a speed of 10 m/s, which the body has after only one second. Option C is wrong because 400 J is the kinetic energy at the moment of throwing, and the potential energy at the top. Option D is wrong because 200 J matches no point of this motion. Exam tip: at the highest point of a vertical throw the speed, and so the kinetic energy, is zero.

The correct answer is D, 0.7 V. A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is. This value is the barrier or knee voltage of a silicon p-n junction: current begins to flow only after the applied voltage crosses about 0.7 V, and after that the drop across the diode stays near 0.7 V while the rest of the supply appears across the resistor. Here 12 V minus 0.7 V, that is 11.3 V, falls across the 240 ohm resistor and fixes the current in the circuit. A germanium diode has a lower knee voltage of about 0.3 V. Option A is wrong because 1.5 V is the voltage of a dry cell and has nothing to do with the junction. Option B is wrong because half the supply would appear across the diode only if it behaved like a resistor of the same value. Option C is wrong because the full 12 V appears across the diode only when it is reverse biased or the circuit is broken. Exam tip: silicon 0.7 V, germanium 0.3 V.

The correct answer is C, 11.2 kilometres per second. Escape velocity is the minimum speed a body must be given so that it leaves the gravitational pull of the planet and never returns. It depends only on the mass and radius of the planet and not on the mass of the body projected or on the direction of projection, and for the earth it works out at about 11.2 kilometres per second.

Option A, about 7.9 kilometres per second, is the orbital velocity for a satellite close to the earth's surface, and it is smaller than the escape velocity by a factor of the square root of two. Option B, 9.8, is the numerical value of the acceleration due to gravity in metres per second squared and has nothing to do with escape velocity except as a familiar number. Option D is far too large for the earth. The moon's escape velocity is only about 2.4 kilometres per second, which is why it cannot retain an atmosphere.

The correct answer is D, Lead and tin. Solder is an alloy of lead and tin, usually in nearly equal parts.

An alloy is a mixture of a metal with one or more other elements, made to gain a property the pure metal lacks. Solder is useful because the mixture melts at a far lower temperature than either lead or tin alone, so it flows easily and is used to join wires and electrical joints. Other alloys asked in papers are brass, made of copper and zinc, bronze of copper and tin, stainless steel of iron, chromium and nickel, and German silver of copper, zinc and nickel.

Option A is wrong because lead with copper is not the soldering alloy. Option B is wrong because tin with iron gives tin plating, used for tin cans. Option C is wrong because lead and iron together are not used as solder.

Exam tip: solder is lead plus tin and melts at a low temperature; brass is copper and zinc, bronze is copper and tin.

The correct answer is B, about 540 calories per gram. This is the heat that one gram of water at a hundred degrees Celsius must absorb to become steam at the same temperature, with no rise in temperature at all; the same quantity is released when steam condenses back to water.

Option A, 80 calories per gram, is the latent heat of fusion of ice, the heat needed to melt one gram of ice at zero degrees, and interchanging the two values is the commonest error in this chapter. Option C, 336, is the same latent heat of fusion expressed in joules per gram rather than calories, offered here with the wrong unit. Option D, 2260, is the latent heat of vaporisation in joules per gram; it is the right quantity in the wrong unit, since 2260 joules is about 540 calories.

The correct answer is D, Thallophyta. Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue. Most algae live in water, make their own food by photosynthesis and reproduce by spores; Spirogyra, Ulothrix, Chara and Volvox are common examples. Option A is wrong because angiosperms are flowering plants whose seeds lie enclosed in a fruit, the most advanced group of all. Option B is wrong because pteridophytes, such as ferns, are the first plants with proper vascular tissue, though they bear no seeds. Option C is wrong because bryophytes, such as mosses and Marchantia, are called the amphibians of the plant kingdom; they stand a step above thallophytes and need water for reproduction. Exam tip: the order of the plant kingdom is Thallophyta, Bryophyta, Pteridophyta, Gymnosperms and Angiosperms.

The correct answer is C, may attract or repel. A magnet cannot be cut into a single north pole and a single south pole. The moment a bar magnet breaks, each piece becomes a complete magnet with a north pole at one end and a south pole at the other, because magnetism comes from the tiny magnetic domains inside the material. So what happens when the pieces are brought close depends only on which ends face each other. If the north end of one faces the south end of the other they attract, and if two like poles face each other they repel. A is wrong because attraction is only one of the two possible results. B is wrong for the same reason, as repulsion happens only with like poles facing. D is wrong because both pieces are still magnets and a force must act between them. Exam tip: magnetic poles always exist in pairs, so every broken piece of a magnet is a smaller full magnet.

The correct answer is A, Archimedes' Principle. It states that the upthrust on a body dipped fully or partly in a fluid equals the weight of the fluid the body pushes aside. This is why a bucket of water feels lighter while it is still in the well, and why a ship of steel floats: its hollow shape displaces enough water to balance its own weight. The principle also gives the law of flotation and is used to find the purity of metals and the density of liquids with a hydrometer. B is wrong because Bernoulli's principle links the speed of a flowing fluid with its pressure, and explains lift on an aeroplane wing. C is wrong because the Beer–Lambert law deals with how much light a solution absorbs as it passes through. D is wrong because Pascal's law says pressure applied to an enclosed fluid is passed on equally in every direction, which is the basis of hydraulic brakes and lifts. Exam tip: Archimedes for buoyancy, Pascal for hydraulic press, Bernoulli for aerofoil lift.

The correct answer is C, Breaking a chalk stick. Force has to be applied to break the chalk because its particles hold one another together, and that pull is the force of attraction between particles.

Every substance is made of particles that attract one another, and the strength of that attraction decides how hard a thing is to break. The attraction is strongest in solids, less in liquids and least in gases, which is why an iron rod needs a hammer, water can be separated with a finger and air offers no resistance at all. The school activity of breaking chalk, then a pencil and then an iron nail shows the difference in this force from one solid to another.

Option A is wrong because compressing a sponge only squeezes out the air in its pores. Option B is wrong because dissolving sugar shows diffusion and the spaces between particles. Option D is wrong because heating ice shows a change of state, not the attraction itself.

Exam tip: attraction between particles is strongest in solids, weaker in liquids and weakest in gases.

The correct answer is A, Platelets. Platelets are the tiny cell fragments that rush to a cut and start the clot. They are also called thrombocytes and are made in the bone marrow from large cells called megakaryocytes. A healthy adult has about 1.5 to 4 lakh platelets per cubic millimetre of blood, and each one lives for only 8 to 10 days. At a wound they stick together to form a plug and release chemicals that turn the soluble protein fibrinogen into fibrin threads, which trap blood cells and seal the leak. B is wrong because plasma proteins such as fibrinogen take part in clotting, but the paper marks platelets as the component that starts and aids clot formation. C is wrong because white blood cells fight infection, not bleeding. D is wrong because red blood cells carry oxygen with haemoglobin. Exam tip: RBC = oxygen, WBC = immunity, platelets = clotting; a falling platelet count is what dengue is known for.

The correct answer is A, 2. A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign. During one half cycle the upper diode conducts and during the next half cycle the lower diode conducts, and both send current through the load in the same direction, so the output has two pulses in every cycle. That is why a full wave rectifier gives a higher average output and a lower ripple than a half wave one. The other way to build a full wave rectifier is the bridge circuit, which uses four diodes but needs no centre tap. Option B is wrong because one diode makes a half wave rectifier that uses only half of each cycle. Option C is wrong because four diodes are used in a bridge rectifier. Option D is wrong because six diodes are used in a three-phase full wave rectifier. Exam tip: half wave 1 diode, centre-tap full wave 2, bridge 4.

The correct answer is B, Adrenal gland. Adrenaline is made by the adrenal glands, which sit like caps on top of the two kidneys. It is released in fear, anger or sudden danger, so it is called the "fight or flight" hormone. It raises the heartbeat and breathing rate, increases blood sugar and sends more blood to the muscles so that the body can react fast. Adrenaline comes from the inner part of the gland, the adrenal medulla; the outer part, the cortex, makes cortisol and aldosterone. A is wrong because the thyroid gland in the neck makes thyroxine, which controls metabolism and needs iodine. C is wrong because the pineal gland in the brain makes melatonin, which controls the sleep-wake cycle. D is wrong because the pituitary gland makes growth hormone and controls several other glands, so it is called the master gland. Exam tip: Adrenal = adrenaline (emergency hormone), Thyroid = thyroxine (metabolism), Pancreas = insulin (blood sugar), Pituitary = master gland.

The correct answer is C, Arthropoda. The name itself says so: in Greek arthros means jointed and podos means foot, so arthropods are the animals with jointed legs. They also have a hard outer skeleton of chitin, a segmented body and an open circulatory system, and they shed the skeleton as they grow, a process called moulting. Arthropoda is the largest phylum in the animal kingdom, holding insects, spiders, scorpions, crabs, prawns, centipedes and millipedes - about eighty out of every hundred known animal species. Option A is wrong because molluscs such as snails, octopus and mussels have a soft body with a muscular foot and usually a shell. Option B is wrong because nematodes are unsegmented roundworms like Ascaris, with no legs at all. Option D is wrong because echinoderms such as starfish and sea urchins are spiny-skinned marine animals that move on tube feet. Exam tip: Arthropoda - jointed legs, chitin skeleton, largest phylum; Mollusca is the second largest.

The correct answer is A, Aedes - Chikungunya - Bacteria. This set is wrong because chikungunya is caused by a virus, the chikungunya virus, and not by bacteria. It is spread by Aedes mosquitoes, the same day-biting mosquitoes that carry dengue and Zika, and it causes high fever with severe joint pain. The name comes from a word in the Makonde language of East Africa meaning 'that which bends up', describing patients bent over with pain. Aedes breeds in clean water stored in coolers, tyres, pots and tanks, which is why dengue and chikungunya cases rise after the monsoon. Option B is a correct set because the Culex mosquito spreads lymphatic filariasis, or elephantiasis, caused by parasitic worms such as Wuchereria bancrofti. Option C is correct because the female Anopheles mosquito spreads malaria, caused by the Plasmodium parasite, a protozoan. Option D is correct because Aedes also spreads dengue, which is caused by the dengue virus. Exam tip: Aedes carries dengue, chikungunya and Zika, all viruses; Anopheles carries malaria; Culex carries filariasis and Japanese encephalitis.

The correct answer is D, uterus. The zygote divides as it travels down the fallopian tube and the resulting ball of cells gets implanted in the thick lining of the uterus.

Fertilisation itself takes place in the fallopian tube, where a sperm fuses with the ovum to form the zygote. Repeated division turns it into an embryo, which reaches the uterus in about a week and sinks into the endometrium, the soft inner wall prepared by hormones. There the placenta develops and supplies the growing embryo with food and oxygen from the mother's blood while carrying away waste. Human pregnancy lasts about nine months.

Option A is wrong because the cervix is only the narrow neck of the uterus that opens into the vagina. Option B is wrong because the ovary produces the ovum and hormones but does not hold the embryo. Option C is wrong because the vagina is the passage that receives the sperm and later serves as the birth canal.

Exam tip: fertilisation in the fallopian tube, implantation in the uterus, nourishment through the placenta.

The correct answer is A, 275 J. Kinetic energy is half m v squared, so half of 22 multiplied by 5 multiplied by 5 gives 275 joules. Kinetic energy is the energy a body has because of its motion. It rises in direct proportion to the mass but with the square of the speed, so doubling the speed makes the energy four times larger, which is why a fast vehicle needs a much longer distance to stop than a slow one. The joule is the SI unit of energy and equals one newton metre; one joule is the work done when a force of one newton moves a body through one metre. Option B is wrong because 110 J is mass multiplied by speed, which gives momentum, not energy, and in different units. Option C is wrong because 1100 J leaves out the half in the formula, that is it works out m v squared. Option D is wrong because 2750 J is ten times the correct value. Exam tip: write half m v squared carefully, because the half and the squared speed are where marks are usually lost.

The correct answer is B, Pascal's law. Pascal's law states that pressure applied to an enclosed fluid is transmitted undiminished in every direction to all parts of the fluid and to the walls of the container. In a hydraulic brake a small force on the narrow master piston creates a pressure that reaches the wider pistons at the wheels, where the same pressure over a larger area gives a much larger force, and all wheels are braked equally at the same moment.

Option A, Archimedes' principle, deals with the upward buoyant force on a body immersed in a fluid and explains ships, submarines and the lactometer. Option C, Bernoulli's principle, relates the speed of a flowing fluid to its pressure and explains the lift of an aerofoil and the working of an atomiser. Option D, Newton's law of gravitation, concerns the attraction between masses. The hydraulic lift and the hydraulic press are the other two standard applications of Pascal's law.

The correct answer is A, conduction and convection. Both of these modes need matter: conduction passes energy from particle to particle and convection carries it by the movement of a fluid. A vacuum has almost no particles, so neither can work across it.

Option B is wrong because radiation travels through a vacuum perfectly well, being an electromagnetic wave; the flask stops it by a different device, the silvering of the facing surfaces, which reflects the radiation back. Option C is incomplete, since the vacuum stops convection as well as conduction. Option D states the opposite of the truth. The stopper of the flask completes the design by preventing the escape of hot vapour, and this three part answer is what examiners look for. The same flask keeps a cold liquid cold for exactly the same reasons, because it blocks heat moving in as well as heat moving out.