Oct/Nov 2019

For which quantity would the magnitude give a reasonable estimate?

Scalars and vectors

Two gliders move directly towards one another along a horizontal air track. Glider P has mass $0.30\ \text{kg}$ and is travelling at a constant speed of $1.2\ \text{m s}^{-1}$. Glider Q has mass $0.60\ \text{kg}$ and is travelling at a constant speed of $1.8\ \text{m s}^{-1}$. The gliders undergo a perfectly elastic collision. What are the speeds of the two gliders after the collision?

Linear momentum and its conservation

A body of weight $W$ hangs from a newton meter. When the body is fully submerged in water, the newton meter gives a reading of $P$. When the body is fully submerged in oil, the newton meter gives a reading of $Q$. Find the ratio $\frac{\text{density of oil}}{\text{density of water}}$?

Density and pressure

Which diagram illustrates a couple?

Turning effects of forces

A body with weight $120\,\text{N}$ is held in equilibrium by two strings, as illustrated. What is the tension $T_1$ in the string on the left?

Equilibrium of forces

Inside a large tank at an oil refinery, three oils with different densities are combined. No chemical reaction takes place. The blend contains: $1200\,\text{kg}$ of oil with density $1100\,\text{kg m}^{-3}$ $1500\,\text{kg}$ of oil with density $860\,\text{kg m}^{-3}$ $4000\,\text{kg}$ of oil with density $910\,\text{kg m}^{-3}$ What is the density of the blend?

Density and pressure

An electric motor delivers $120\,\text{W}$ of useful mechanical output power. The motor has an efficiency of $60\%$. Which row is the correct one?

Potential difference and power

A fixed quantity of gas is taken through a sequence of pressure and volume changes. For two of the changes, neither the gas nor its surroundings do any work. For one change, the gas does work on the surroundings. For another change, the surroundings do work on the gas. What is the amount of work done on the gas during the change in which the surroundings do work on the gas?

Energy conservation

An object moving at a speed of $10\,\text{m s}^{-1}$ has a kinetic energy of $1500\,\text{J}$. Its speed is then raised to $40\,\text{m s}^{-1}$. What is the object’s new kinetic energy?

Gravitational potential energy and kinetic energy

A car engine applies a force of $600\,\text{N}$ to move the car through $1.0\,\text{km}$ in $150\,\text{s}$. What is the mean useful output power of the engine?

Energy conservation

A graph showing extension against force for a spring is displayed. What is the spring constant of the spring?

Elastic and plastic behaviour

A wave’s speed in deep water is determined by its wavelength $L$ and the acceleration of free fall $g$. Which equation could represent the speed $v$ of the wave?

Progressive waves

A force stretches a wire. The graph indicates how the extension of the wire changes with the applied force. At first, a force $W$ produces an extension of $d$. The force is then raised to $2W$. The extension then becomes $2d$. Which area on the graph shows the work done by the force as the force rises from $W$ to $2W$?

Elastic and plastic behaviour

A transverse wave travelling along a rope has wavelength $\lambda$ and period $T$. The graph illustrates how the displacement of the rope particles varies with distance in the direction of wave travel at time $t = 0$. Particle $X$ is marked. Which graph shows how the displacement of particle $X$ changes with time $t$?

Progressive waves

Which statement is correct for every type of transverse wave?

Transverse and longitudinal waves

Source S produces microwaves with a steady amplitude. The microwaves strike a metal screen P and are reflected. A stationary wave is set up between S and P. The wavelength of the microwaves is much less than the separation between S and P. A detector Q is then moved slowly and at a constant speed from S to P. What happens to the amplitude of the signal detected by Q?

Stationary waves

A siren on a police car that is moving produces a sound wave with frequency of $440\,\text{Hz}$. An observer who is not moving detects sound with frequency of $494\,\text{Hz}$. The speed of sound in air is $340\,\text{m s}^{-1}$. What might be the car’s speed and direction of travel?

Doppler effect for sound waves

An electromagnetic wave travels in a vacuum with a wavelength of $138\,\text{pm}$. Which region of the electromagnetic spectrum is this wave part of?

Electromagnetic spectrum

A pair of wave pulses moves towards one another along a long rope. Each pulse has the same amplitude and wavelength, and both travel at a speed of $0.50\,\text{m s}^{-1}$. The diagram indicates the rope at time $t = 0$. Which diagram represents the rope at time $t = 3.0\,\text{s}$?

Progressive waves

Water waves with wavelength $\lambda$ strike an obstacle at right angles and pass through a narrow opening. The opening has width equal to $\lambda$. The waves leaving the opening spread out through an angle $\theta$, as shown. The opening is then gradually made wider. Which changes, if any, happen to $\theta$ and to the wavelength of the waves that emerge?

Diffraction

Monochromatic light of wavelength $720\,\text{nm}$ from laser X is directed normally at a diffraction grating, and a diffraction pattern is formed. Light from laser Y is then also directed normally at the same grating. The third-order maximum produced by laser Y appears at the same position as the second-order maximum produced by laser X. What is the wavelength of the light from laser Y?

The diffraction grating

A diffraction grating with line spacing $d$ is illuminated by monochromatic light of frequency $f$. The speed of light is $c$. Which expression may be used to find the greatest order of intensity maximum formed by the grating?

The diffraction grating

The diagram depicts two vectors $X$ and $Y$, drawn to scale. Given that $X = Y - Z$, which diagram most accurately shows vector $Z$?

Scalars and vectors

A metal plate with constant thickness is linked to a cell, as illustrated. Electrons travel in a clockwise direction round the circuit. Which statement about the metal plate is correct?

Electric current

The diagram indicates the direction of current through a metal block. Charge carriers enter the block via the face PQRS and exit from the face opposite it. The number density of charge carriers is $n$. Each charge carrier carries charge $e$. The mean drift speed of the charge carriers is $v$. Which expression gives the current in the block?

Electric current

Which quantity cannot be used as a unit for potential difference?

Potential difference and power

Which graph could be used to represent how the resistance $R$ of a filament lamp changes as the applied potential difference (p.d.) $V$ is increased up to the normal operating p.d.?

Resistance and resistivity

Kirchhoff’s two laws for electric circuits can be obtained by applying conservation laws. Which conservation laws form the basis of Kirchhoff’s laws?

Kirchhoff's laws

The diagram illustrates a circuit. Which statement concerning the circuit is incorrect?

Practical circuits

The diagram illustrates a circuit that has four voltmeters. Their readings are $V_1$, $V_2$, $V_3$ and $V_4$. Every reading is positive. Which equation linking the voltmeter readings is correct?

Kirchhoff's laws

The network contains a $3.0\,\Omega$ resistor together with two $6.0\,\Omega$ resistors, as illustrated. The potential difference (p.d.) across the network is $4.0\,\text{V}$. What current flows through the $3.0\,\Omega$ resistor?

Resistance and resistivity

In the circuit diagram, every resistor is identical and each ammeter has negligible resistance. The reading $A_1$ is $0.6\,\text{A}$. What readings do the other ammeters show?

Kirchhoff's laws

A nucleus of an element that is unstable decays by releasing either an $\alpha$-particle or a $\beta^-$ particle, forming a nucleus of a different element. That nucleus is also unstable and likewise releases either an $\alpha$-particle or a $\beta^-$ particle. This sequence goes on until an isotope of the original element is formed. What is the least possible number of these particles emitted?

Atoms, nuclei and radiation

A student wants to measure, as accurately as possible, the diameter of a wire (known to be about $1\ \text{mm}$) and the internal diameter of a pipe (known to be about $2\ \text{cm}$). Which instruments would be most suitable for the student to use for these measurements?

Errors and uncertainties

The diagrams display the quark makeup of four different hadrons. One of the hadrons is a $\Sigma^+$ particle. Its charge is $+e$, with $e$ representing the elementary charge. Which hadron could be the $\Sigma^+$ particle?

Fundamental particles

For a resistor with resistance $R$, the power $P$ lost as heat is found from $P = \frac{V^2}{R}$, where $V$ represents the potential difference (p.d.) across the resistor. The percentage uncertainty in $V$ is $5\%$ and the percentage uncertainty in $R$ is $2\%$. What is the percentage uncertainty in $P$?

Errors and uncertainties

The velocity-time graph for an object with mass $2.5\ \text{kg}$ is shown. What resultant force acts on the object?

Momentum and Newton's laws of motion

Which statement is a direct consequence of Newton’s first law?

Momentum and Newton's laws of motion

A resultant force makes an object accelerate. What does the resultant force equal?

Momentum and Newton's laws of motion

A skydiver leaves an aircraft that is travelling horizontally. The vertical component of the skydiver’s velocity is $v$. The vertical component of the skydiver’s acceleration is $a$. Which row best describes $v$ and $a$ in the first few seconds after the skydiver leaves the aircraft?

Equations of motion

A cyclist is moving at $5\,\text{m s}^{-1}$ and a small car is moving at $12\,\text{m s}^{-1}$. Which statement is not a sensible estimate?

Errors and uncertainties

A positively charged oil droplet is descending through air in a uniform electric field directed vertically upwards. The droplet moves at a constant terminal speed $v_0$, and the electric field has strength $E$. The magnitude of the air resistance force on the droplet is proportional to the droplet’s speed. Which graph shows how $v_0$ varies with $E$?

Momentum and Newton's laws of motion

A rigid uniform bar, $2.4\,\text{m}$ long, is supported horizontally by a pivot at its midpoint. Weights are suspended from two positions on the bar as illustrated in the diagram. A couple has to be applied to keep the bar in equilibrium. What is the torque and direction of this couple?

Turning effects of forces

An object is acted on by two coplanar forces, as illustrated. Which diagram represents the resultant $F$ of these two forces?

Scalars and vectors

Four measuring cylinders are each filled with the same liquid up to the heights shown. In which position is the pressure greatest?

Density and pressure

A gas in an engine carries out work on a piston whose cross-sectional area is $80\,\text{cm}^2$. The piston is under a constant pressure of $4.6 \times 10^5\,\text{Pa}$. What amount of work is done by the gas on the piston as it travels a distance of $25\,\text{cm}$?

Density and pressure

A power station that burns coal as its fuel has a mean power output of $3000\,\text{MW}$. Every day, coal is delivered by $20$ trains. The station’s efficiency in changing the thermal energy given out by the coal into electrical energy is $26\%$. When $1.0\,\text{kg}$ of coal is burned, it releases $33\,\text{MJ}$ of thermal energy. What mass of coal is carried by each train?

Energy conservation

A cylinder made of wood is floating in a bath of water with part of it below the surface. A force $F$ is applied to the cylinder until it is completely submerged. Which statement is not correct?

Density and pressure

A crane’s motor lifts a load with mass $600\,\text{kg}$. The load moves upward at a steady speed of $12\,\text{m min}^{-1}$. What is the useful power output of the motor?

Gravitational potential energy and kinetic energy

The graph illustrates the effect on a spring of a force applied, with the force increasing to a maximum of $5.0\,\text{N}$. The spring follows Hooke’s law for forces up to $7.0\,\text{N}$. What total extension does the spring produce when a force of $7.0\,\text{N}$ is applied?

Elastic and plastic behaviour

A rubber cord is suspended from a rigid support. A load fixed to its lower end is increased gradually from zero, then decreased gradually back to zero. The force-extension curve for contraction lies below the force-extension curve for stretching. What is represented by the shaded region between the curves?

Elastic and plastic behaviour

Which expression represents an SI base quantity?

SI units

A transverse wave is moving along a rope. The wave has a frequency of $2.0\,\text{Hz}$. The graph illustrates how the wave displacement varies with distance at time $t = 0$. Which diagram represents the wave’s position at time $t = 0.5\,\text{s}$?

Progressive waves

These two graphs describe the same wave. Graph 1 shows how displacement varies with time at one fixed distance. Graph 2 shows how displacement varies with distance at a single moment in time. What is the wave speed?

Progressive waves

A microphone is connected to a cathode-ray oscilloscope (CRO). A tuning fork is struck and then placed beside the microphone, producing the waveform shown on the CRO screen. The CRO time-base setting is $2.00\,\text{ms}$ per division. What is the most suitable estimate of the frequency of the sound made by the tuning fork?

Progressive waves

A loudspeaker producing a steady frequency of $2000\,\text{Hz}$ is moved in a horizontal circle at a speed of $15.0\,\text{m s}^{-1}$. A stationary observer, positioned level with the loudspeaker and far away from it, hears sound whose frequency changes. The greatest frequency heard is $2097\,\text{Hz}$. Determine the speed of sound in air.

Doppler effect for sound waves

Two electromagnetic waves have wavelengths of $5.0 \times 10^{-7}\,\text{m}$ and $5.0 \times 10^{-2}\,\text{m}$. Which row states the parts of the electromagnetic spectrum that these waves are in?

Electromagnetic spectrum

An electromagnetic-wave transmitter is positioned $45\,\text{cm}$ away from a reflective surface. The waves it emits have a frequency of $1.00\,\text{GHz}$. A stationary wave forms, with a node at the transmitter and another node at the surface. How many antinodes lie in the region between the transmitter and the surface?

Stationary waves

Which of the following statements about a light wave and a sound wave is correct?

Transverse and longitudinal waves

A concert held outdoors has two large speakers positioned next to the stage to play music. To check the speakers, they are set to produce sound with the same wavelength and the same amplitude. The curved lines on the diagram show wavefronts. At which point is the sound loudest?

Interference

An electromagnetic wave is directed normally onto a diffraction grating. A second-order maximum appears at an angle of $30^{\circ}$ to a normal to the grating. The grating contains $5000$ lines per $\text{cm}$. What is the wavelength of the wave?

The diffraction grating

P is shown as a point close to charge X. If a negatively charged test charge is placed at point P, it is observed to be repelled by X with a force directed radially away from X. Which arrow shows the correct direction of the electric field at point P due to charge X?

Scalars and vectors

Which list is made up entirely of scalar quantities?

Scalars and vectors

An oil drop of mass $m$, carrying $n$ extra electrons, remains at rest in the uniform electric field between two horizontal plates that are separated by distance $d$. The potential difference across the plates is $V$, the elementary charge is $e$ and the free-fall acceleration is $g$. What is the value of $n$?

Potential difference and power

For a wire carrying a current of $5.0\,\text{A}$, the mean drift speed of the conduction electrons is $7.4 \times 10^{-4}\,\text{m s}^{-1}$. Which row shows a possible cross-sectional area and number of conduction electrons per unit volume for this wire?

Electric current

A fixed resistor with resistance $12\,\Omega$ is connected to a battery. A current of $0.20\,\text{A}$ flows through the resistor. The current is then doubled. What is the new power dissipated in the resistor?

Potential difference and power

An electric current flows through a resistor for an unknown duration. Which two quantities may be used to determine the energy dissipated by the resistor?

Potential difference and power

Two cells, with electromotive forces $E_1$ and $E_2$ and internal resistances $r_1$ and $r_2$, are connected to a resistor $R$ as shown. The terminal potential difference across cell 1 is zero. Which expression gives the resistance of resistor $R$?

Kirchhoff's laws

A battery possesses an electromotive force (e.m.f.) $E$ and an internal resistance $r$. It supplies a current $I$ to a variable resistor, and the potential difference (p.d.) across the battery terminals is $V$. The variable resistor is then altered so that $I$ becomes larger. Why does $V$ fall?

Potential difference and power

Three identical resistors are arranged between terminals P and Q in three different networks X, Y and Z, as illustrated. What is the order of increasing total resistance between P and Q, starting with the lowest?

Resistance and resistivity

The diagram depicts a variable resistor $R$ together with two fixed resistors joined in series in a circuit so that they function as a potential divider. The cell with electromotive force (e.m.f.) $6.0\text{ V}$ has negligible internal resistance. A cell with e.m.f. $2.0\text{ V}$ and a galvanometer are linked into the potential divider. As the resistance of $R$ is changed, the galvanometer shows zero. What is the resistance of resistor $R$?

Potential dividers

The table shows some information about four neutral (uncharged) atoms W, X, Y and Z. Two of these atoms are isotopes of the same element. What is the proton number of this element?

Atoms, nuclei and radiation

Which particle is not a fundamental particle?

Fundamental particles

A micrometer is used to measure the $28.50\,\text{mm}$ width of a plastic ruler. The micrometer gives a reading to the nearest $0.01\,\text{mm}$. How should this measurement be recorded correctly?

Errors and uncertainties

A nucleus that is not stable undergoes decay and gives off a $\beta^-$ particle. What, if anything, happens to the nucleus’s quark composition?

Atoms, nuclei and radiation

A wooden block’s sides are measured using calipers. The side lengths are found to be $20.0\,\text{mm}$, $40.0\,\text{mm}$ and $10.0\,\text{mm}$. The calipers have an absolute uncertainty of $\pm 0.1\,\text{mm}$. What is the percentage uncertainty in the calculated volume of the block?

Errors and uncertainties

A ball is launched straight up from ground level and rises to a greatest height of $12.7\,\text{m}$ before returning to the ground. Take air resistance to be negligible. What is the total time that the ball spends in the air?

Equations of motion

A snooker ball has a mass of $200\,\text{g}$. It strikes the cushion on a snooker table and then rebounds along the same line. When it reaches the cushion, the ball is moving at $14.0\,\text{m s}^{-1}$, and after the collision it moves away at $7.0\,\text{m s}^{-1}$. The ball remains in contact with the cushion for $0.60\,\text{s}$. What is the average force exerted on the ball by the cushion?

Momentum and Newton's laws of motion

A tennis ball is let go from rest at time $t = 0$ and then drops through air for a long period. Which graph of displacement $s$ against time $t$ shows the motion of the ball most accurately?

Non-uniform motion

Rosetta, a space probe, was built to study a comet. It had two parts: an orbiter and a lander. The orbiter’s mass was $170\,\text{kg}$ and the lander’s mass was $100\,\text{kg}$. During separation, the lander was driven towards the comet’s surface, giving it a change in velocity towards the comet of $3.0\,\text{m s}^{-1}$. Treat the orbiter and lander as an isolated system. As the separation occurred, the orbiter moved away from the comet. What change in speed did the orbiter have?

Linear momentum and its conservation

Which quantity is paired with the correct unit?

SI units

A solid sphere with a density lower than that of water is kept fully submerged in water several metres beneath the surface. The water has a uniform density. The sphere is then released. Right after it is let go, the sphere moves upwards. Which row correctly states how the upthrust on the sphere and the resultant force on the sphere change?

Density and pressure

The diagram illustrates two pairs of parallel forces, X and Y. Which statement is correct?

Turning effects of forces

A heavy ball suspended from a cable is kept in equilibrium by a chain, as illustrated. Which vector diagram represents the three forces acting on the ball?

Equilibrium of forces

At sea level, atmospheric pressure is $100\,\text{kPa}$, while the density of air is $1.3\,\text{kg m}^{-3}$. Suppose that the density of air falls linearly with height above sea level. Based on this, what estimate can be made for the atmosphere’s total height?

Density and pressure

Trains deliver coal to a power station. The table lists the quantities that describe how the power station operates: average output of the power station $P$ (unit W); number of trains each day $N$; mass of coal carried on a train $M$ (unit kg); energy released by $1\,\text{kg}$ of coal $E$ (unit J); number of seconds in one day $S$. Which expression represents the efficiency of the power station?

Energy conservation

A piston in a gas supply pump has an area of $500\,\text{cm}^2$ and it travels a distance of $30\,\text{cm}$. The pump pushes the gas against a constant pressure of $4000\,\text{Pa}$. How much work is done by the piston?

Density and pressure

A steel ball falls through oil at constant speed. Which graph illustrates how the gravitational potential energy $E_p$ and the kinetic energy $E_k$ of the ball change with time?

Gravitational potential energy and kinetic energy

A car moving along a horizontal road has a maximum useful output power of $P$. The overall resistive force on the car is $kv^2$, where $v$ is the car’s speed and $k$ is a constant. Which equation is correct when the car is moving at maximum speed?

Non-uniform motion

At the start, four identical uniform blocks, each of mass $m$ and thickness $h$, lie spread out on a table. The acceleration of free fall is $g$. What amount of work is done on the blocks when they are piled one on top of another?

Gravitational potential energy and kinetic energy

A stress-strain graph for a wire is shown. What is the Young modulus of the material from which the wire is made?

Stress and strain

Which two units are not equal to one another?

SI units

The diagram presents a force-extension graph for a rubber band as the band is stretched and then the stretching force is reduced to zero. What can be deduced from this graph?

Elastic and plastic behaviour

Which statement concerning light waves and sound waves is incorrect?

Transverse and longitudinal waves

The graph shows a sound wave. Which statement is correct?

Transverse and longitudinal waves

A cathode-ray oscilloscope (CRO) is being used to show a wave with frequency $5.0\,\text{kHz}$. The screen image is shown. What time-base setting is the CRO using?

Practical circuits

A siren produces sound with frequency $1000\,\text{Hz}$. The siren is travelling at $20\,\text{m s}^{-1}$ towards an observer who is stationary. The speed of sound in air is $330\,\text{m s}^{-1}$. Which expression gives the frequency heard by the observer correctly?

Doppler effect for sound waves

A sound source with constant power $P$ is placed in open space. The sound intensity $I$ at a distance $r$ from this source is given by $I = \dfrac{P}{4\pi r^2}$. In what way does the amplitude $a$ of the vibrating air molecules change as the distance $r$ from the source increases?

Progressive waves

To show a stationary wave, two microwave transmitters, each producing waves of wavelength $4\,\text{cm}$, are positioned opposite one another, as illustrated. A detector is then dragged along a straight path between the transmitters. It finds positions where the signal is greatest and where it is least. The detector is a distance $d$ from the transmitter on the left. Assume that both transmitters lie at antinodes of the stationary wave. Which row gives a value of $d$ for a maximum and for a minimum?

Stationary waves

The graph illustrates how the height of the water surface at a location in a harbour changes with time $t$ as waves move past that location. What are $p$ and $q$?

Progressive waves

The diagram shows a sketch of a wave pattern over a brief time interval. Which description of the wave is correct?

Progressive waves

The double-slit experiment shows interference from two coherent sources of light waves. In the diagram, the curved lines show wavefronts. At which point does complete destructive interference (a minimum) take place?

Interference

The arrow shows vector $\vec{R}$. Which diagram does not show $\vec{R}$ as two components at right angles to each other?

Scalars and vectors

Light with wavelength $567\,\text{nm}$ falls perpendicularly on a diffraction grating. The grating contains $400$ lines per mm. Several diffraction maxima are seen on the opposite side of the grating. What is the angular separation between the second-order maximum and the third-order maximum?

The diffraction grating

The diagram illustrates the electric field pattern between two point charges, $P$ and $Q$, that are opposite in sign and unequal in magnitude. Which statement about the charges is correct?

Potential difference and power

A uniform electric field is shown by five horizontal field lines. P and Q are two points within the field. Because of the field, a positively charged particle in a vacuum travels from P to Q. Which statement has to be true?

Potential difference and power

An electrical conductor made of metal has a resistance of $5.6\,\text{k}\Omega$. A potential difference (p.d.) of $9.0\,\text{V}$ is applied between its two ends. How many electrons pass a point in the conductor in one minute?

Electric current

As shown, a battery of electromotive force (e.m.f.) $12\,\text{V}$ and negligible internal resistance is linked to three resistors, each with resistance $6.0\,\Omega$. Calculate the power dissipated in resistor $R$.

Potential difference and power

A circuit contains a box with two electrical components inside it. The variable resistor is altered and readings are recorded to find the $I$-$V$ characteristic of the box, as illustrated. Which combination of two electrical components inside the box would match the measured $I$-$V$ characteristic most closely?

Practical circuits

A cell with internal resistance $0.5\,\Omega$ is connected to a fixed resistor with resistance $10\,\Omega$. The resistor’s resistance is then altered to $20\,\Omega$. Which statement is not correct?

Practical circuits

Which row gives the correct description of Kirchhoff’s laws?

Kirchhoff's laws

In the circuit diagram shown, every resistor is the same. The meter reading $V_1$ is $8.0\,\text{V}$, while the meter reading $V_2$ is $1.0\,\text{V}$. What values do the remaining voltmeters show?

Potential dividers

A radioactive nucleus releases an $\alpha$-particle or a $\beta^-$ particle, forming a new product nucleus. Which decay could have produced the product nucleus given?

Atoms, nuclei and radiation

How might systematic errors be reduced?

Errors and uncertainties

Which of the following statements is correct?

Physical quantities

For a resistor, the power loss $P$ is given by $P = \frac{V^2}{R}$. The percentage uncertainty in the potential difference $V$ is $3\%$ and the percentage uncertainty in the resistance $R$ is $2\%$. What percentage uncertainty does $P$ have?

Errors and uncertainties

A lead sphere is dropped from rest at point X, far above the surface of a planet. The sphere moves in a vacuum. After $4.0\ \text{s}$, it has travelled a vertical distance of $3.0\ \text{m}$. Assume that the acceleration of free fall remains constant. What distance from point X will the sphere have travelled after $20\ \text{s}$ from release?

Equations of motion

As shown, a box is at rest on the Earth. Newton’s third law explains that forces of the same kind occur in pairs. One force in such a pair is the weight $W$ of the box. Which arrow shows the other force in this pair?

Momentum and Newton's laws of motion

A snowflake is descending through the sky on a calm day. Its weight acts vertically downwards, while air resistance acts vertically upwards. During the fall, the air resistance rises until it matches the weight, so there is no resultant force acting on the snowflake. Once the two forces are equal, which statement is correct?

Momentum and Newton's laws of motion

In an isolated system, two objects X and Y undergo a perfectly elastic collision. Their velocities before and after the collision are shown. What is the speed $v$ of Y following the collision?

Linear momentum and its conservation