▶️ Answer/Explanation
Detailed solution:
To find out who ran the second lap the fastest, we need to calculate the time interval for the second lap only by subtracting the time at the end of the first lap from the time at the end of the second lap.
For athlete A, the time is $56 – 26 = 30$ seconds. For athlete B, it is $55 – 27 = 28$ seconds.
For athlete C, the second lap takes $60 – 28 = 32$ seconds, and for athlete D, it takes $54 – 28 = 26$ seconds.
Comparing these results, athlete D has the lowest time for the second lap ($26$ seconds).
Since a lower time for the same distance indicates a higher speed, athlete D is the fastest runner for that specific lap.
▶️ Answer/Explanation
Detailed solution:
To determine if the car is increasing in speed, we need to look at the distance covered in each consecutive time interval.
In this data set, the computer records the total distance at $0.5$ s, $1.0$ s, $1.5$ s, and $2.0$ s.
If the speed is increasing, the car should travel a greater distance in each subsequent $0.5$ s interval compared to the previous one.
Looking at Option C, the distances covered are $15$ m, $35$ m ($+20$ m), $60$ m ($+25$ m), and $90$ m ($+30$ m).
Since the gap between the distances is getting larger every half-second, it proves the car is accelerating.
In contrast, constant gaps would mean constant speed, and decreasing gaps would mean the car is slowing down.
▶️ Answer/Explanation
Detailed solution:
To solve this, we need to identify two distinct physical concepts: the constant for Earth’s gravity and the fundamental definition of velocity.
The gravitational field strength on Earth is a standard value used in physics calculations, approximately $9.8$ $\text{N/kg}$, which is often rounded to $10$ $\text{N/kg}$ in many introductory curricula.
Velocity is a vector quantity, meaning it accounts for both the rate of motion and the specific direction of that motion.
Unlike speed, which is just distance over time, velocity is defined specifically as the rate of change of displacement.
Looking at the table, Row D correctly identifies the field strength as $10$ $\text{N/kg}$ and provides the correct definition for velocity.
Therefore, Option D is the only row where both pieces of information are scientifically accurate.
▶️ Answer/Explanation
Detailed solution:
Weight is fundamentally defined as the force acting on an object due to gravity.
While mass is an intrinsic property that represents the amount of matter in an object, weight is a force measured in Newtons ($N$).
Option A is incorrect because gravitational force per unit mass actually defines the gravitational field strength, $g$.
Options C and D are common misconceptions; an object still possesses weight as long as it is within a gravitational field, even if it is in freefall or in orbit.
Therefore, the most accurate description is that weight is simply the gravitational pull exerted on that specific object.
Mathematically, this relationship is expressed by the formula $W = m \cdot g$.
▶️ Answer/Explanation
Detailed solution:
To solve this, we first need to determine the extension required to reach the target length. The extension is calculated by subtracting the original length ($2.0\text{ cm}$) from the new length ($6.0\text{ cm}$), which gives us an extension of $4.0\text{ cm}$.
Looking at the provided load-extension graph, we locate the value of $4.0\text{ cm}$ on the vertical axis (Extension).
By moving horizontally from the $4.0\text{ cm}$ mark to the plotted line and then dropping down to the horizontal axis, we can find the corresponding load.
The graph shows that an extension of $4.0\text{ cm}$ corresponds exactly to a load of $1.0\text{ N}$.
Therefore, a $1.0\text{ N}$ load is what increases the total length of the spring to $6.0\text{ cm}$.
▶️ Answer/Explanation
Detailed solution:
When two solid surfaces are in contact and try to move relative to one another, a resistive force is generated that acts in the opposite direction of the motion.
This specific force is known as friction, and it arises due to the microscopic roughness and molecular attractions between the two surfaces.
While gravity and weight are vertical forces acting toward the center of the Earth, they do not inherently oppose horizontal sliding motion between surfaces.
Kinetic is a term used to describe energy or a type of friction (kinetic friction), but it is not the name of a fundamental force itself.
Therefore, friction is the correct term for the force that actively works to resist or stop the sliding movement between two solids.
▶️ Answer/Explanation
Detailed solution:
To calculate the work done against gravity, we use the standard formula $W = F \times d$, where the force is the weight of the object and the distance is the vertical height gained.
In this problem, the weight of the box is given directly as $20 \text{ N}$, which represents the downward force of gravity we must overcome.
The vertical height of the stairs is $1.2 \text{ m}$, while the horizontal distance of $1.8 \text{ m}$ is irrelevant for calculating work done against gravity.
Therefore, we multiply the weight ($20 \text{ N}$) by the vertical displacement ($1.2 \text{ m}$) to find the energy transferred.
This leads us to the calculation $20 \times 1.2$, making Option B the correct choice.
▶️ Answer/Explanation
Detailed solution:
To find which submarine experiences the most pressure, we use the liquid pressure formula: $P = \rho gh$, where $\rho$ is the density, $g$ is gravity, and $h$ is the depth.
From this equation, we can see that pressure is directly proportional to both the density of the liquid and the depth of the object.
Comparing the types of water, sea water has a higher density ($1020 kg/m^3$) than fresh water ($1000 kg/m^3$), so we should look at the sea water options first.
Between the two submarines in sea water, the one at a depth of $40 m$ is deeper than the one at $20 m$.
Since submarine D is in the densest fluid at the maximum depth shown, it will experience the greatest pressure.
Therefore, Option D is the correct choice based on these physical principles.
▶️ Answer/Explanation
Detailed solution:
To identify the processes, we need to look at the direction of the arrows between the different states of matter.
Process $2$ shows the transition from a liquid to a solid; this phase change is known as freezing or solidification, where energy is released.
Process $3$ represents the change from a liquid to a gas, which occurs when a substance is heated and is known as boiling or evaporation.
By observing the provided table, Option A correctly matches process $2$ with freezing and process $3$ with boiling.
Processes $1$ and $4$ (though not specifically asked for in the final selection) represent melting and condensing respectively.
Therefore, selecting the row that accurately describes these physical changes leads us directly to the first option.
▶️ Answer/Explanation
Detailed solution:
To convert a temperature from the Celsius scale to the Kelvin (absolute) scale, we use the standard conversion formula where $T(K) = \theta(^{\circ}C) + 273$.
In this specific problem, we are given the melting point of copper as $1100$ °C.
By substituting the given value into our formula, we calculate the absolute temperature as $1100 + 273$.
Performing the addition gives us a final value of $1373$ K.
Therefore, when expressing the thermal state of copper at its melting point in SI units, $1373$ K is the correct thermodynamic temperature, which corresponds to Option C.
▶️ Answer/Explanation
Detailed solution:
When the flask is placed in ice, the temperature of both the glass container and the liquid inside begins to decrease.
Most substances undergo thermal contraction when cooled because the particles lose kinetic energy and move closer together, occupying less volume.
In this scenario, level Y is lower than level X, which indicates that the total volume of the liquid has decreased.
While the glass flask also contracts slightly, liquids generally expand and contract much more significantly than solids for the same change in temperature.
Therefore, the drop in level from X to Y is primarily caused by the liquid contracting as it cools down to the temperature of the ice.
This makes Option C the correct explanation for the observed change in the tube.
▶️ Answer/Explanation
Detailed solution:
To solve this, we need to consider the standard melting and boiling points of pure water at atmospheric pressure, which are $0$°C and $100$°C respectively.
At $-10$°C, which is well below the freezing point, water exists in a solid state as ice.
At $50$°C, the temperature is between the melting and boiling points, meaning the water has melted but not yet turned to steam, so it is a liquid.
At $110$°C, the temperature has exceeded the boiling point of $100$°C, so the water has completely changed into a gaseous state (steam).
Looking at the table, Row C correctly identifies these states as solid, liquid, and gas for the respective temperatures.
▶️ Answer/Explanation
Detailed solution:
Evaporation is a surface phenomenon that occurs at temperatures below the boiling point.
Unlike boiling, which happens throughout the entire volume of the liquid, evaporation only takes place at the surface where molecules can break free into the air.
For a molecule to escape, it must possess enough kinetic energy to overcome the attractive intermolecular forces holding it in the liquid phase.
The molecules with the highest energy are the ones most likely to “jump” out of the surface, leaving behind the slower, cooler molecules.
Therefore, only high-energy molecules at the surface can escape, making Option C the correct description of this process.
▶️ Answer/Explanation
Detailed solution:
To prevent the student from burning their hand, the spoon must be made of a material that does not transfer heat quickly from the hot liquid to the handle.
Materials like wood or plastic are classified as insulators because they have a very low rate of thermal conduction.
Metals, on the other hand, are good conductors of heat due to the presence of free electrons that transfer energy rapidly through the material.
Therefore, choosing an insulator ensures that the thermal energy remains mostly in the liquid rather than traveling up the spoon.
Looking at the table, Option D is the only one that correctly identifies the material as an insulator and provides the correct scientific explanation for why the hand stays safe.
▶️ Answer/Explanation
Detailed solution:
Thermal radiation consists of electromagnetic waves, specifically in the infrared spectrum, which do not require a physical medium to transfer energy.
Unlike conduction and convection, which rely on particles in solids, liquids, or gases, radiation can travel through the vacuum of space.
Because these waves can pass through any transparent medium as well as empty space, they effectively move through air, water, and a vacuum.
If radiation couldn’t travel through a vacuum, heat from the Sun would never reach the Earth.
Therefore, all three conditions listed—air, vacuum, and water—allow for the passage of thermal radiation, making option A the correct choice.
▶️ Answer/Explanation
Detailed solution:
To find the wavelength, we look at the total distance covered by the waves, which is the radius of the pond, $3.0$ m. Since there are $10$ whole waves in this distance, the wavelength $\lambda$ is calculated as $3.0 \text{ m} / 10 = 0.30 \text{ m}$.
For the frequency, we consider how many waves are produced per second. The problem states that $10$ waves reach the edge in $5.0$ s.
Frequency $f$ is the number of waves divided by the total time, so $f = 10 / 5.0 \text{ s} = 2.0 \text{ Hz}$.
By checking these two values, we can determine that the wavelength is $0.30 \text{ m}$ and the frequency is $2.0 \text{ Hz}$.
This matches the data provided for Option B.
▶️ Answer/Explanation
Detailed solution:
In a longitudinal wave, the particles of the medium vibrate back and forth in a direction that is parallel to the direction in which the wave energy travels.
This means the direction of vibration and the direction of propagation are along the same line, rather than being at right angles to each other.
A classic example of a longitudinal wave is a sound wave, where air molecules compress and rarefy as the sound moves forward.
In contrast, light waves and water waves are transverse, as their vibrations occur at $90^\circ$ to the direction of travel.
Looking at the provided table, Option C correctly identifies the parallel nature of the vibration and provides sound as the correct example.
▶️ Answer/Explanation
Detailed solution:
In the study of optics, we use specific terms to describe how light interacts with a surface.
The line labeled $Z$ is the “normal,” which is an imaginary line drawn perpendicular ($90^{\circ}$) to the mirror’s surface at the point of incidence.
The angle $x$ is the “angle of incidence,” defined as the angle between the incoming (incident) ray and the normal.
Similarly, the angle $y$ is the “angle of reflection,” which is the angle between the reflected ray and the normal line.
According to the laws of reflection, the angle of incidence $x$ is always equal to the angle of reflection $y$.
By matching these definitions to the provided table, we can see that Row A correctly identifies all three components.
▶️ Answer/Explanation
Detailed solution:
By looking at the ray diagram, we can see that the object is placed at a distance greater than twice the focal length ($u > 2f$) from the converging lens.
The rays of light actually meet on the opposite side of the lens, which tells us that the image formed is a real image.
We can observe that the image is formed below the principal axis, meaning it is inverted compared to the object.
Furthermore, the height of the image is clearly smaller than the height of the object, making it diminished in size.
Therefore, the characteristics of the image are real, inverted, and diminished, which corresponds to Option A.
▶️ Answer/Explanation
Detailed solution:
When white light enters a glass prism, it slows down and changes direction, a general process known as refraction.
However, different colors of light have different wavelengths, causing them to refract by slightly different angles; for instance, violet light bends more than red light.
This specific phenomenon, where white light is separated into its constituent colors (the visible spectrum), is called dispersion.
While refraction is the cause, “dispersion” is the specific name for the splitting effect described in the question.
Therefore, the correct term to identify this process is dispersion, making Option B the correct choice.
▶️ Answer/Explanation
Detailed solution:
To solve this, we need to match the specific biological hazards to the correct parts of the electromagnetic spectrum.
Ionizing radiation like $\gamma$-rays (gamma rays) has high energy and can penetrate deep into tissues to cause cell mutation and cancer.
Ultraviolet (UV) radiation is higher in energy than visible light and is well known for damaging the surface of the skin, leading to painful skin burns.
Internal heating occurs when molecules, particularly water in body cells, absorb lower-energy radiation such as microwaves.
By looking at the table, we see that row C correctly identifies $\gamma$-rays for mutation, ultraviolet for skin burns, and microwaves for internal heating.
Therefore, Option C is the only choice that accurately aligns each hazard with its corresponding radiation type.
▶️ Answer/Explanation
Detailed solution:
To find the depth of the shoal, we first recognize that the total time given ($1.2$ s) is for a round trip—the sound travels down to the fish and then back up to the boat.
We can calculate the total distance traveled by the sound using the formula $\text{distance} = \text{speed} \times \text{time}$.
Substituting the values, we get $1500 \text{ m/s} \times 1.2 \text{ s} = 1800$ m for the entire journey.
Since this distance represents twice the depth (down and up), we must divide it by $2$ to find the actual distance to the fish.
Therefore, the depth is $1800 \text{ m} / 2 = 900$ m, which makes Option B the correct answer.
▶️ Answer/Explanation
Detailed solution:
Sound waves are mechanical waves that travel through a medium as longitudinal waves, characterized by compressions and rarefactions.
The human range of hearing is generally considered to be between 20Hz and 20 000Hz.
In this case, both the initial frequency of 31 000Hz and the final frequency of 32 000Hz are well above the upper limit of human audibility.
Such waves are classified as ultrasound, meaning they are beyond what a human ear can detect regardless of the change in pitch.
Therefore, because sound is longitudinal and the frequencies provided are outside our hearing range, the wave cannot be heard.
This confirms that Option C is the correct description of the wave’s nature and its perception.
▶️ Answer/Explanation
Detailed solution:
To solve this, we need to remember that magnetic field lines always point away from the North pole (N) and toward the South pole (S).
A compass needle is essentially a small bar magnet where the arrow head represents the North-seeking pole.
Since opposite poles attract and like poles repel, the North pole of the compass will be repelled by the magnet’s North pole and attracted to its South pole.
Looking at diagram C, the compass near the N pole points away from it, and the compass near the S pole points toward it.
This correctly aligns with the direction of the magnetic field lines surrounding a bar magnet, making Option C the correct choice.
▶️ Answer/Explanation
Detailed solution:
When a current flows through the coil, it creates a magnetic field that magnetizes the metal bar inside.
The fact that the bar can pick up and hold nails indicates that it has become a magnet; this process is known as induced magnetism.
Because the nails drop off immediately when the current is switched off, it means the bar loses its magnetism just as quickly as it gained it.
Materials that are easily magnetized but lose their magnetism once the external field is removed are called “soft” magnetic materials.
Soft iron is the classic example used for this purpose, making it the material of the bar and the phenomenon an example of induced magnetism as per row B.
▶️ Answer/Explanation
Detailed solution:
Electrical power $P$ represents the rate at which energy is transferred or dissipated in a component.
By definition, power is the product of the potential difference $V$ across the component and the current $I$ flowing through it.
This relationship is derived from the fact that $V$ is energy per unit charge and $I$ is the rate of flow of charge.
While other formulas like $P = I^2R$ or $P = \frac{V^2}{R}$ are also valid by substituting Ohm’s Law, the fundamental equation given in the options is $P = IV$.
Therefore, Option B is the correct mathematical representation for power dissipated by the resistor.
▶️ Answer/Explanation
Detailed solution:
Electrical conductors are materials that allow electric charges to flow through them easily, typically due to the presence of free electrons.
Metals are generally excellent conductors because of their metallic bonding structure.
In the given list, aluminium, iron, and silver are all metals and therefore serve as good conductors of electricity.
Plastic, on the other hand, is a polymer where electrons are tightly bound, making it an effective insulator rather than a conductor.
Since three out of the four materials listed are metals, the correct group of conductors is aluminium, iron, and silver.
This matches Option A, as it correctly identifies all the metallic substances in the student’s test.
▶️ Answer/Explanation
Detailed solution:
To solve this, we need to look at Ohm’s Law, which is expressed by the formula V=IR, where V is the potential difference, I is the current, and R is the resistance.
According to the question, the resistance R of the variable resistor is being increased.
If we want the current I to stay exactly the same (constant), we have to look at how V must change to balance the equation.
Since R is getting larger, the product of I×R will naturally increase if I remains unchanged.
Therefore, to maintain that balance, the potential difference V must also be increased proportionally.
This makes Option B the only mathematically and physically sound choice.
▶️ Answer/Explanation
Detailed solution:
In Diagram 1, the circuit has a single resistor with a resistance value of $R$.
When an identical resistor is added in parallel, as shown in Diagram 2, the total or combined resistance of the circuit decreases.
Mathematically, the combined resistance $R_p$
▶️ Answer/Explanation
Detailed solution:
A fuse is a critical safety component designed to protect an electrical circuit from excessive current.
It must always be connected to the live wire because this is the wire that carries the high voltage into the appliance.
If a fault occurs and the current becomes too high, the fuse wire melts and breaks the circuit, immediately cutting off the electricity supply.
By placing it in the live wire, we ensure that the appliance is isolated from the high-voltage source, making it safe for the user.
If the fuse were in the neutral wire and it blew, the appliance could still be “live” and potentially cause an electric shock even if it isn’t working.
▶️ Answer/Explanation
Detailed solution:
In a d.c. motor, the force F acting on the wire in a magnetic field is given by the relationship F=BIL, where B is the magnetic field strength, I is the current, and L is the length of the wire.
This means the force is directly proportional to both the current through the coil (F∝I) and the strength of the magnetic field (F∝B), which would result in straight-line graphs passing through the origin.
Increasing the number of turns in the coil also linearly increases the total force because each turn experiences the same force, contributing to the overall turning effect.
However, graph D suggests that increasing the resistance of the coil would increase the force, which is incorrect.
According to Ohm’s Law, I=V/R, so increasing the resistance actually decreases the current, which in turn reduces the force F. Therefore, graph D does not show the correct trend.
▶️ Answer/Explanation
Detailed solution:
The fundamental structure of an atom consists of a central nucleus and orbiting subatomic particles. The nucleus contains protons, which have a positive charge, and neutrons, which carry no charge at all; this makes the overall charge of the nucleus positive.
Electrons, which carry a negative charge, move in the space around this central nucleus.
While the atom as a whole is usually neutral because the number of positive protons equals the number of negative electrons, the internal arrangement always pairs a positive center with negative outer particles.
Therefore, we say that negative electrons surround a positive nucleus.
This electrostatic attraction between the opposite charges is what holds the atom together, making Option B the only scientifically accurate description.
▶️ Answer/Explanation
Detailed solution:
By definition, isotopes are atoms of the same element that contain the same number of protons but different numbers of neutrons.
Since they belong to the same element, their atomic number (Z) remains identical, which is why statement D is always correct.
While some isotopes can be radioactive or unstable, many occur naturally as stable forms, so statements A and B are not true for all isotopes.
Statement C is incorrect because it is the variation in the number of neutrons that actually distinguishes one isotope from another.
Therefore, having the same number of protons is the fundamental requirement for any group of isotopes of a single element.
▶️ Answer/Explanation
Detailed solution:
Ionising radiation comes from both natural background sources and man-made activities.
Many naturally occurring foods and drinks contain tiny amounts of radioactive isotopes, such as Potassium-40 or Carbon-14, which contribute to our internal radiation dose.
Options B, C, and D involve non-ionising radiation or chemical processes that do not emit nuclear radiation.
Greenhouse gases affect the climate, while mobile masts and TV transmissions use low-energy radio waves and microwaves.
Therefore, ingestion of food and drink is the only factor listed that directly adds to a person’s annual ionising radiation exposure.
▶️ Answer/Explanation
Detailed solution:
To solve this, we first look at the penetrating power of different types of radiation. Alpha particles are stopped by paper, and beta particles are stopped by a few millimeters of aluminum, but only gamma radiation can pass through 10 mm of lead (though it is partially attenuated).
Since the radiation successfully passes through the lead sheet in the question, the source must be emitting gamma rays.
Next, we consider the nature of gamma radiation; unlike alpha or beta particles, gamma rays are electromagnetic waves and carry no electric charge.
Because they are neutral, they are not deflected or attracted by electric fields and will continue to travel in a straight line.
Therefore, the correct combination is that the radiation is gamma and it is not deflected, which corresponds to Option D.
▶️ Answer/Explanation
Detailed solution:
The process of mixing radioactive waste with liquid glass, known as vitrification, is primarily used to ensure long-term containment.
Radioactive decay rates and half-lives are intrinsic properties of a nucleus and cannot be changed by physical or chemical processes like mixing with glass.
By solidifying the waste into a glass block, we ensure it becomes chemically stable and physically immobile, preventing it from leaking into the environment or groundwater.
Storing these blocks in steel drums provides an additional barrier against radiation and physical damage.
Transparency is irrelevant here, as the focus is purely on safety and preventing contamination over thousands of years.
Therefore, Option C is the correct answer as it addresses the containment aspect of waste management.
▶️ Answer/Explanation
Detailed solution:
In our solar system, planets are generally divided into two main groups: the inner rocky planets and the outer gas giants.
The four rocky planets, also known as terrestrial planets, are Mercury, Venus, Earth, and Mars, which all have solid silicate surfaces.
Jupiter and Saturn are classified as gas giants, consisting mostly of hydrogen and helium without a well-defined solid surface.
Uranus and Neptune are considered ice giants because they are composed mostly of elements heavier than hydrogen and helium, like oxygen and nitrogen.
Since Venus is one of the four inner planets with a solid, rocky crust, it is the correct answer.
Therefore, among the given choices, Venus is the only one that fits the classification of a rocky planet.
▶️ Answer/Explanation
Detailed solution:
The Moon does not produce its own light; we see it because it reflects sunlight.
As the Moon orbits the Earth, our perspective of the illuminated half changes depending on its position relative to the Sun and the Earth.
When the Moon is between the Earth and Sun, the dark side faces us, but as it moves along its path, we begin to see different portions of the lit surface.
This cycle of changing appearances is what we refer to as the phases of the Moon.
Therefore, it is the movement of the Moon around the Earth that causes these visual shifts over a period of approximately 29.5 days.
This makes Option C the correct explanation for the lunar cycle.
▶️ Answer/Explanation
Detailed solution:
The Universe is defined as the entirety of space, time, matter, and energy, encompassing everything that exists.
Options B, C, and D all describe components that are part of our local Solar System, which is just a tiny fraction of a single galaxy.
In reality, the Universe is vast and contains many billions of galaxies, each of which contains millions or billions of stars.
While stars and planets are part of the Universe, they are organized into these massive galactic structures spread across space.
Therefore, saying the Universe is made up of billions of galaxies is the most accurate description of its true scale and composition.
▶️ Answer/Explanation
Detailed solution:
The Sun is a massive sphere of glowing gas, and its composition is dominated by the two lightest elements in the periodic table.
Approximately 73% of the Sun’s mass is made up of hydrogen, while helium accounts for nearly 25%.
These gases serve as the fuel for nuclear fusion, where hydrogen nuclei fuse together to form helium, releasing vast amounts of energy in the process.
Other elements like oxygen, carbon, and neon exist only in very trace amounts, totaling less than 2% of the solar mass.
Therefore, the Sun is primarily a mixture of hydrogen and helium gases, making Option A the correct choice.
Understanding this composition is fundamental to studying how stars generate light and heat over billions of years.