General Science Mixed Quiz: Set 11

The correct answer is B, the second law. It states that the rate of change of momentum of a body is proportional to the applied force and takes place in the direction of the force. Since momentum is mass times velocity, the rate of its change for a body of constant mass is mass times acceleration, which gives the equation force equals mass times acceleration.

Option A, the first law, tells us only that a body keeps its state unless an unbalanced force acts, and so defines force without measuring it. Option C, the third law, deals with the pairing of action and reaction on two different bodies. Option D belongs to a different branch of the subject altogether. The second law also gives the definition of the newton, which is the force that gives a mass of one kilogram an acceleration of one metre per second squared.

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 B, half of mass into the square of the speed. Kinetic energy is the energy a body has because of its motion, and it grows with the square of the speed, so a body moving twice as fast carries four times the kinetic energy.

Option A is the expression for gravitational potential energy near the surface of the Earth, that is mass into acceleration due to gravity into height, and it depends on position rather than motion. Option C, mass into speed, is the linear momentum of the body, a vector quantity measured in kilogram metre per second, not an energy at all. Option D leaves out the factor of one half and is the standard careless error in this question. Remember also that kinetic energy can be written as the square of momentum divided by twice the mass.

The correct answer is A, the law of inertia. The first law states that a body continues in its state of rest or of uniform motion in a straight line unless an unbalanced external force acts on it, which is exactly the property called inertia.

Option B refers to the second law, which deals with the rate of change of momentum and yields the equation force equals mass times acceleration. Option C is the third law, which says that action and reaction are equal and opposite and act on different bodies. Option D, the law of gravitation, is a separate law of Newton's, stating that every body attracts every other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them. The first law also defines force, by telling us that a force is what is needed to change a state of motion.

The correct answer is D, Elaioplasts. Leucoplasts are the colourless plastids of plant cells, and each kind is named after what it stores. Elaioplasts are the leucoplasts that make and store oils and fats, and they are plentiful in the tapetum, the nourishing layer of cells in the anther that feeds developing pollen grains and leaves an oily coat on them. The other leucoplasts are amyloplasts, which store starch in potato tubers and cereal grains, and proteinoplasts, which store protein. Option A is wrong because gerontoplasts are chloroplasts that have aged, as in a leaf turning yellow in autumn. Option B is wrong because proteinoplasts, also called aleuroplasts, hold protein and not oil. Option C is wrong because chloroplasts are green, pigment-bearing plastids that carry out photosynthesis, so they are not leucoplasts at all. Exam tip: name the leucoplast by its store — amyloplast for starch, elaioplast for oil (elaion is Greek for oil), proteinoplast for protein.

The correct answer is B, joule. Work is the product of force and displacement, so its unit is the newton metre, which is given the name joule; one joule of work is done when a force of one newton moves a body through one metre in its own direction. Energy is measured in the same unit, because work done is energy transferred.

Option A, the newton, is the SI unit of force alone. Option C, the watt, is the unit of power, that is the rate of doing work, and equals one joule per second. Option D, the pascal, is the unit of pressure and equals one newton per square metre. Candidates who confuse the joule with the watt lose marks in the very next question of a paper, so learn the pair as work in joule and power in watt.

The correct answer is B, linear momentum. Before firing, the gun and the bullet are at rest, so the total momentum of the system is zero. No external force acts along the barrel, so the total must stay zero: the bullet leaves with a large forward momentum and the gun acquires an equal momentum backwards, which is felt as the recoil. Because the gun is far heavier than the bullet, its backward velocity is small.

Option A, energy, is conserved in the wider sense but does not by itself give the direction and size of the recoil. Option C, mass, and option D, charge, are also conserved quantities but are irrelevant here. The same principle explains rocket propulsion, where hot gases are pushed out at high speed and the rocket moves the other way, and it is equally the third law of motion seen from another side.

The correct answer is D, Golgi apparatus. The Golgi apparatus is the main site where glycoproteins and glycolipids are formed. It is a stack of flat, disc-shaped sacs called cisternae, first described by Camillo Golgi in 1898. Proteins made on the endoplasmic reticulum reach the Golgi, where sugars are added to them, and they are then packed into vesicles and sent to places inside the cell or out of it. That is why the Golgi is called the packaging and dispatch centre of the cell, and it also helps to form lysosomes. Option A is wrong because plastids, such as chloroplasts, carry out photosynthesis or store food and pigments in plant cells. Option B is wrong because lysosomes are small sacs of digestive enzymes and are called the suicide bags of the cell. Option C is wrong because mitochondria make energy in the form of ATP and are called the powerhouse of the cell. Exam tip: Golgi means packaging and adding sugars; mitochondria mean ATP; a lysosome is the suicide bag.

The correct answer is B, watt. Power is the rate of doing work, that is work divided by the time taken, so its unit is the joule per second, which is named the watt after James Watt. A machine of one kilowatt does one thousand joule of work every second.

Option A, the joule, measures work or energy, not the rate at which it is delivered. Option C, the newton second, is the unit of impulse and of momentum. Option D, the kilowatt hour, is a unit of energy in spite of its name, because it is a power multiplied by a time; it is the commercial unit of electricity and equals 3.6 million joule. The confusion between the watt and the kilowatt hour is deliberate in many papers, so keep the distinction of rate against quantity clear.

The correct answer is C, more than the atmospheric pressure. Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air. During expiration the diaphragm relaxes and moves up into its dome shape, and the intercostal muscles between the ribs relax, so the ribs move down and inward. This reduces the volume of the chest cavity, which raises the pressure in the lungs and pushes the air out. Inspiration is the reverse: the diaphragm contracts and flattens, the chest cavity grows, lung pressure falls below atmospheric pressure and air rushes in. Option A is wrong because when the pressures are equal no air moves; this happens for a moment between breaths. Option B is wrong because lower pressure inside the lungs draws air in, which is inspiration. Option D is wrong because contraction of the diaphragm enlarges the chest and causes inspiration, not expiration. Exam tip: inspiration means the diaphragm contracts and lung pressure falls; expiration means it relaxes and lung pressure rises.

The correct answer is C, the kilogram metre per second. Momentum is the product of mass and velocity, so its unit is the unit of mass multiplied by the unit of velocity, that is kilogram multiplied by metre per second. It is a vector, pointing in the direction of the velocity.

Option A, the newton, is the unit of force, which is the rate of change of momentum rather than momentum itself; a newton is in fact one kilogram metre per second squared. Option B, the joule, is the unit of work and energy. Option D, the newton per second, is not a standard unit at all, although newton second is an acceptable alternative form for momentum because force multiplied by time equals change of momentum, the quantity called impulse. That link between impulse and momentum is itself a favourite examination point.

The correct answer is B, Thyroid, Adrenal glands, Pituitary. The pituitary gland sends out hormones that order the thyroid and the adrenal glands to release their own hormones. The pituitary is a pea-sized gland attached to the base of the brain, and it is called the master gland because it controls several other endocrine glands. For example, it releases a thyroid-stimulating hormone that makes the thyroid produce thyroxine, and another hormone that makes the adrenal glands release theirs. NCERT's Class 8 science book notes that glands such as the thyroid and the adrenals secrete hormones on receiving a message from the pituitary. A is wrong because the pancreas releases insulin in response to blood sugar, and the thyroid does not command the other two. C is wrong because the testes and ovaries take their orders from the pituitary, not from the thyroid. D is wrong because the pituitary gives orders; it does not wait for orders from the thyroid. Exam tip: pituitary, master gland; thyroid, thyroxine; adrenal, adrenaline; pancreas, insulin.

The correct answer is C, 746 watt. The horsepower is an older unit of power that survives in the rating of motors and vehicles, and one horsepower is taken as about 746 watt, that is roughly three quarters of a kilowatt.

Option A, 100 watt, is close to the rating of an old filament bulb and has no connection with the horsepower. Option B, 500 watt, is simply half a kilowatt and is offered as a plausible round figure. Option D, 1000 watt, is one kilowatt; a common mistake is to treat the horsepower and the kilowatt as equal, when in fact one kilowatt is about 1.34 horsepower. The figure 746 is worth memorising exactly, because the question is often set in reverse, asking how many watt a motor of a given horsepower consumes.

The correct answer is B, Falciparum. Plasmodium falciparum causes malignant, or cerebral, malaria, the most dangerous form of the disease. Red blood cells infected by it become sticky and block the small blood vessels of the brain and other organs, which can lead to coma and death if treatment is delayed. Malaria spreads through the bite of the female Anopheles mosquito; the parasite first multiplies in the liver and then in red blood cells, and the bursting of these cells brings the cycles of chills and high fever. Ronald Ross proved the mosquito link in 1897 while working in India and won the Nobel Prize in 1902. Option A is wrong because P. vivax causes benign tertian malaria, which can relapse from dormant stages in the liver but is rarely fatal. Option C is wrong because P. ovale causes a mild tertian malaria found mainly in Africa. Option D is wrong because P. malariae causes quartan malaria, with fever every fourth day. Exam tip: falciparum = malignant; vivax = benign but relapsing; female Anopheles = vector.

The correct answer is B, inertia of motion. While the bus is moving, the passenger's whole body moves with it. When the brakes are applied, the feet stop along with the floor of the bus, but the upper body tends to keep moving forward at the same speed, and the passenger is thrown forward.

Option A, inertia of rest, explains the opposite case: a passenger falls backward when a stationary bus starts suddenly, because the body tends to remain at rest. Option C, inertia of direction, explains why mud flies off tangentially from a spinning wheel or why a passenger leans outward when the bus turns. Option D, centripetal force, is the force directed towards the centre that keeps a body on a circular path and has nothing to do with braking in a straight line. All three kinds of inertia are asked through everyday examples like these.

The correct answer is C, Thymine. In DNA, adenine always pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three. This is called complementary base pairing, and it is why one strand of DNA can be used to copy the other. The double-helix model was proposed by James Watson and Francis Crick in 1953, using X-ray images made by Rosalind Franklin. Adenine and guanine are purines with two rings, while thymine and cytosine are pyrimidines with one ring, so each pair has the same width and the helix stays even. In RNA, thymine is replaced by uracil. Option A is wrong because guanine is a purine like adenine and pairs with cytosine. Option B is wrong because cytosine pairs with guanine through three hydrogen bonds. Option D is wrong because histone is a protein around which DNA is wound in chromosomes; it is not a base at all. Exam tip: A pairs with T by two bonds, G with C by three; RNA has U in place of T.

The correct answer is C, the kilowatt hour. Household electricity is billed in these units, and one kilowatt hour, popularly called one unit, is the energy consumed when an appliance of one kilowatt runs for one hour; in SI terms it equals 3.6 million joule.

Option A, the joule, is the SI unit of energy but is far too small for billing, since even a single fan uses millions of joule in an evening. Option B, the watt, measures power and not energy, so it cannot be billed at all. Option D, the erg, is the CGS unit of work and is smaller still, with ten million erg in one joule. Questions on this topic often ask for the number of joule in one kilowatt hour, so carry the figure 3.6 million along with the name.

The correct answer is A. The three equations of uniformly accelerated motion are v equals u plus at, s equals ut plus half of a t squared, and v squared equals u squared plus twice a s, where u is the initial velocity, v the final velocity, a the acceleration, t the time and s the distance covered.

Option B replaces time with distance in the first equation, which is wrong because the first equation connects velocity with time, not with distance. Option C omits the half and squares nothing, so it is not the second equation. Option D squares the time in the first equation, which belongs to the second equation instead. The third equation is the useful one when time is not given, and the choice of equation in a numerical question is decided entirely by which of the five quantities the problem does not mention.

The correct answer is B, four times. Kinetic energy is half the mass into the square of the speed, so when the speed is multiplied by two the energy is multiplied by two squared, that is four. If the speed were tripled the energy would become nine times as large.

Option A, double, would be right only if the energy varied directly with the speed, which is true of momentum, not of kinetic energy. Option C, half, describes what happens to nothing in this situation and is pure distraction. Option D, unchanged, would be true only if the speed did not change, as in uniform circular motion. This relation explains why the braking distance of a vehicle rises sharply with speed, a point road safety questions also use.

The correct answer is B, displacement. On a velocity-time graph the height of the curve is velocity and the base is time, so the area enclosed is velocity multiplied by time, which is displacement.

Option A, acceleration, is given by the slope of the same graph, not by its area, and mixing up slope and area is the commonest error in this question. Option C, force, and option D, momentum, cannot be read off a velocity-time graph at all unless the mass of the body is also given. The companion result is worth learning in the same breath: on a distance-time graph the slope gives the speed, so a straight sloping line means uniform speed and a horizontal line means the body is at rest. Papers often show a simple graph and ask for one of these three readings.