While releasing the arrow from a stretched bow, the Potential Energy of the bow is converted into?

The correct answer is C, increase in area of contact reduces pressure exerted. Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure. The weight of the bag stays exactly the same whether the strap is thin or wide, but a wide strap spreads that weight over more of the shoulder, so the shoulder feels less pressure and the strap does not cut into the skin. The same idea explains why school bags, seat belts and the wide tyres of a tractor are made broad. A is wrong because it states the relation upside down, since pressure falls when area rises. B and D are wrong because the force is simply the weight of the load and the width of the strap cannot change it; only the pressure changes. Exam tip: P equals F divided by A, so broad straps and flat feet reduce pressure while sharp knives and pointed nails increase it.

The correct answer is D, the statement that atmospheric pressure is negligible. Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all. We do not feel it because the pressure of the blood and other fluids inside the body pushes outward with the same force, and the two balance. A is a correct statement because pressure is force divided by area, so the same force on a smaller area gives more pressure, which is why knives are sharpened and nails are pointed. B is correct because a liquid presses in every direction, on the bottom as well as on the side walls, and the push grows with depth. C is correct because the column of air above us has weight and therefore presses on us. Exam tip: P equals force divided by area; atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal.

The correct answer is B, sulphurous acid. Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3. Sulphur dioxide is an oxide of a non-metal, and such oxides are acidic in nature, which is why the solution turns blue litmus red. The same gas, released when coal and diesel burn, dissolves in rain water in the air and is then slowly oxidised further, so sulphur dioxide is one of the main causes of acid rain. A is wrong because sulphur trioxide is made by oxidising sulphur dioxide with more oxygen over a catalyst, not by dissolving it in water. C is wrong because sulphuric acid is formed when sulphur trioxide, and not sulphur dioxide, meets water. D is wrong because sulphur is the element itself and cannot be got back simply by dissolving its oxide. Exam tip: SO2 with water gives H2SO3; SO3 with water gives H2SO4.

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 C, remains same. Loudness and frequency are two different properties of sound. Loudness depends on the amplitude of the vibration, that is how far the vibrating part moves from its rest position, while frequency is the number of vibrations made in one second and is measured in hertz. Turning the volume up makes the speaker push the air harder, so the amplitude and therefore the loudness rise, but the tune still plays the same notes, so the frequency does not change. This is why the ringtone sounds stronger and not higher in pitch. A and B are wrong because a change in frequency would change the pitch, and a louder ringtone would then sound shriller or deeper, which does not happen. D is wrong because the relation is definite and well known, so it can certainly be decided. Exam tip: amplitude decides loudness, frequency decides pitch, and the speed of sound in air depends only on the medium.