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Cambridge IAL Physics study materials
Cambridge IAL Physics study resources

Cambridge IAL Physics practice questions

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Question 1Main theoretical concepts fundamental to physics

A ball is thrown vertically upwards and returns to the thrower's hand. Neglecting air resistance, which quantity remains constant throughout the flight?

  1. The acceleration of the ball Correct answer.
  2. The horizontal component of velocity
  3. The velocity of the ball
  4. The kinetic energy of the ball

Explanation

Once the ball has left the hand, the only force acting is its weight, so by Newton's second law the acceleration is constant at g directed downwards. Velocity, speed and kinetic energy all change continuously during the flight, and the horizontal component is zero throughout, so it is not a meaningful constant here.

Question 2Main theoretical concepts fundamental to physics

Which statement about the base SI units of the newton is correct?

  1. 1 N = 1 kg m⁻¹ s⁻²
  2. 1 N = 1 kg m s⁻² Correct answer.
  3. 1 N = 1 kg m² s⁻²
  4. 1 N = 1 kg m s⁻¹

Explanation

Newton's second law gives F = ma, so one newton is the force that gives a mass of one kilogram an acceleration of one metre per second squared. Substituting the base units of mass and acceleration gives kg m s⁻². The other combinations correspond to momentum, energy and a dimensionally incorrect expression.

Question 3Main theoretical concepts fundamental to physics

A car travels 150 m in 10 s while accelerating uniformly from rest. What is its acceleration?

  1. 3.0 m s⁻² Correct answer.
  2. 15 m s⁻²
  3. 7.5 m s⁻²
  4. 1.5 m s⁻²

Explanation

Using s = ut + ½at² with u = 0 gives 150 = ½ × a × 100, so a = 300/100 = 3.0 m s⁻². The final speed would be 30 m s⁻¹, which confirms the average speed of 15 m s⁻¹ over the interval.

Question 4Main theoretical concepts fundamental to physics

A skydiver falls at terminal velocity. Which statement about the forces on the skydiver is correct?

  1. The resultant force equals the weight
  2. The air resistance is greater than the weight
  3. The air resistance equals the weight Correct answer.
  4. The weight is zero

Explanation

Terminal velocity means zero acceleration, so by Newton's second law the resultant force must be zero. The upward drag therefore exactly balances the downward weight. The weight is never zero, and if drag exceeded weight the skydiver would decelerate.

Question 5Main theoretical concepts fundamental to physics

A 2.0 kg trolley moving at 3.0 m s⁻¹ collides with a stationary 4.0 kg trolley and they stick together. What is their common velocity after the collision?

  1. 0.50 m s⁻¹
  2. 1.5 m s⁻¹
  3. 2.0 m s⁻¹
  4. 1.0 m s⁻¹ Correct answer.

Explanation

Momentum is conserved in the collision: (2.0 × 3.0) = (2.0 + 4.0) × v, so 6.0 = 6.0v and v = 1.0 m s⁻¹. Kinetic energy is not conserved in a perfectly inelastic collision, so momentum is the appropriate conservation law.

Question 6Main theoretical concepts fundamental to physics

Which quantity is defined as the rate of doing work?

  1. Power Correct answer.
  2. Impulse
  3. Efficiency
  4. Momentum

Explanation

Power is defined as the rate of transfer of energy, that is work done per unit time, measured in watts. Impulse is force multiplied by time, momentum is mass multiplied by velocity, and efficiency is a ratio of useful output to total input energy.

Question 7Main theoretical concepts fundamental to physics

A wave has frequency 50 Hz and wavelength 4.0 m. What is its speed?

  1. 54 m s⁻¹
  2. 200 m s⁻¹ Correct answer.
  3. 0.08 m s⁻¹
  4. 12.5 m s⁻¹

Explanation

The wave equation v = fλ gives v = 50 × 4.0 = 200 m s⁻¹. Frequency is the number of oscillations per second and wavelength is the distance travelled per oscillation, so their product is the distance travelled per second.

Question 8Main theoretical concepts fundamental to physics

In a transverse progressive wave, what is the direction of oscillation of the particles relative to the direction of energy transfer?

  1. Parallel to the direction of energy transfer
  2. At 45° to the direction of energy transfer
  3. Randomly oriented relative to the direction of energy transfer
  4. Perpendicular to the direction of energy transfer Correct answer.

Explanation

By definition, in a transverse wave the particles oscillate perpendicular to the direction in which the wave travels and carries energy. Parallel oscillation defines a longitudinal wave, such as sound in air. The particles themselves do not travel along with the wave.

Question 9Main theoretical concepts fundamental to physics

Two identical resistors of resistance 6.0 Ω are connected in parallel across a 12 V supply of negligible internal resistance. What is the total current drawn from the supply?

  1. 4.0 A Correct answer.
  2. 8.0 A
  3. 2.0 A
  4. 1.0 A

Explanation

Two equal resistors in parallel have a combined resistance of 3.0 Ω. The current is then I = V/R = 12/3.0 = 4.0 A, which is also twice the 2.0 A that flows through each branch.

Question 10Main theoretical concepts fundamental to physics

A potential divider consists of a 4.0 kΩ resistor in series with a 12 kΩ resistor across a 16 V supply. What is the potential difference across the 12 kΩ resistor?

  1. 4.0 V
  2. 10 V
  3. 16 V
  4. 12 V Correct answer.

Explanation

The total resistance is 16 kΩ, so the current is 16 V / 16 kΩ = 1.0 mA. Across the 12 kΩ resistor the p.d. is 1.0 mA × 12 kΩ = 12 V. Equivalently, the 12 kΩ resistor takes 12/16 of the supply voltage.

Question 11Main theoretical concepts fundamental to physics

A wire of resistance R is stretched uniformly so that its length doubles while its volume stays constant. What is the new resistance?

  1. 2R
  2. 4R Correct answer.
  3. R/4
  4. R/2

Explanation

Constant volume means doubling the length halves the cross-sectional area. Since R = ρL/A, doubling L and halving A multiplies the resistance by 2 × 2 = 4. The resistivity itself is a property of the material and does not change.

Question 12Main theoretical concepts fundamental to physics

Photoelectrons are emitted from a metal surface only when the incident light exceeds a certain minimum frequency. Which statement explains this threshold?

  1. Each photon must supply at least the work function energy to release an electron Correct answer.
  2. Each photon must supply energy equal to the kinetic energy of the electron
  3. The light must be polarised before it can eject electrons
  4. The intensity of the light must exceed a fixed minimum value

Explanation

In the photon model, one photon is absorbed by one electron and must provide at least the work function to escape the metal. Any surplus appears as kinetic energy, as described by hf = φ + E_k. Intensity controls the number of photons per second, not the energy of each photon.

Question 13Main theoretical concepts fundamental to physics

The nucleus of an atom of ²³⁸₉₂U undergoes alpha decay. Which nucleus is produced?

  1. ²³⁴₉₂U
  2. ²³⁸₉₁Pa
  3. ²³⁸₉₀Th
  4. ²³⁴₉₀Th Correct answer.

Explanation

An alpha particle is a helium nucleus, ⁴₂He, so the parent loses 4 from its nucleon number and 2 from its proton number. This gives nucleon number 234 and proton number 90, which is thorium-234. Beta decay would instead raise the proton number by one.

Question 14Main theoretical concepts fundamental to physics

In a nuclear fission reactor, what is the function of the moderator?

  1. It removes heat from the reactor core
  2. It absorbs neutrons to stop the chain reaction
  3. It slows fast neutrons so that they can induce further fission Correct answer.
  4. It shields the surroundings from gamma radiation

Explanation

Fission releases fast neutrons, but uranium-235 is far more likely to fission with slow (thermal) neutrons, so the moderator reduces their kinetic energy through repeated collisions. Control rods, not the moderator, absorb neutrons to regulate the rate. Coolant and shielding are separate components.

Question 15Main theoretical concepts fundamental to physics

An ideal gas in a sealed rigid container is heated. Which statement correctly describes what happens to its molecules?

  1. Their average speed decreases while the pressure stays constant
  2. Their average kinetic energy decreases because the volume is fixed
  3. Their average kinetic energy increases while the number of molecules stays constant Correct answer.
  4. Their average kinetic energy stays constant while the number of molecules increases

Explanation

For a fixed mass of gas in a rigid container the number of molecules is constant. Heating raises the mean translational kinetic energy, which is proportional to thermodynamic temperature, so the pressure rises at constant volume.

Question 16Main theoretical concepts fundamental to physics

A gas is compressed slowly at constant temperature. Which statement about the gas is correct?

  1. The product of pressure and volume stays constant Correct answer.
  2. The internal energy increases as the volume decreases
  3. The pressure decreases as the volume decreases
  4. Heat must be supplied to the gas during compression

Explanation

Boyle's law states that for a fixed mass of ideal gas at constant temperature, pV is constant, so reducing the volume raises the pressure. Because the temperature does not change, the internal energy of an ideal gas stays constant, and work done on the gas is balanced by heat released to the surroundings.

Question 17Main theoretical concepts fundamental to physics

A simple pendulum of length 0.90 m oscillates with small amplitude on the Earth's surface, where g = 9.8 m s⁻². What is its period?

  1. 6.0 s
  2. 3.8 s
  3. 1.9 s Correct answer.
  4. 0.30 s

Explanation

For a simple pendulum, T = 2π√(L/g) = 2π√(0.90/9.8) ≈ 2π × 0.303 ≈ 1.9 s. The period is independent of the mass of the bob and, for small amplitudes, independent of the amplitude.

Question 18Main theoretical concepts fundamental to physics

A body moves in a horizontal circle at constant speed. Which statement about the forces on it is correct?

  1. The resultant force acts along the tangent to the circle
  2. The resultant force acts away from the centre of the circle
  3. The resultant force is zero because the speed is constant
  4. The resultant force acts towards the centre of the circle Correct answer.

Explanation

Although the speed is constant, the velocity direction changes continuously, so there is a centripetal acceleration directed towards the centre. By Newton's second law the resultant force, mv²/r, must also point towards the centre. This force is provided by tension, friction or gravity depending on the situation.

Question 19Main theoretical concepts fundamental to physics

A 0.20 kg mass on a spring oscillates with amplitude 5.0 cm and angular frequency 20 rad s⁻¹. What is the maximum kinetic energy of the mass?

  1. 0.010 J Correct answer.
  2. 0.020 J
  3. 0.20 J
  4. 0.10 J

Explanation

The maximum speed is v₀ = ωA = 20 × 0.050 = 1.0 m s⁻¹. The maximum kinetic energy is then ½mv₀² = ½ × 0.20 × 1.0² = 0.010 J, which equals the total energy of the oscillation.

Question 20Main theoretical concepts fundamental to physics

Two coherent sources produce an interference pattern. Which condition produces destructive interference at a point?

  1. The path difference is an odd number of half wavelengths Correct answer.
  2. The waves arrive with a phase difference of zero
  3. The path difference from the two sources is a whole number of wavelengths
  4. The waves from the two sources have different frequencies

Explanation

Destructive interference requires the waves to arrive in antiphase, which for coherent sources corresponds to a path difference of (n + ½)λ, an odd number of half wavelengths. A whole-number path difference gives constructive interference. Coherence, meaning a constant phase relationship, is essential for a stable pattern.

Question 21Main theoretical concepts fundamental to physics

Light of wavelength 600 nm passes through a diffraction grating with 5.0 × 10⁵ lines per metre. What is the angle of the first-order maximum?

  1. 30.0°
  2. 35.0°
  3. 8.6°
  4. 17.5° Correct answer.

Explanation

The slit spacing is d = 1/(5.0 × 10⁵) = 2.0 × 10⁻⁶ m. Using d sin θ = nλ with n = 1 gives sin θ = 600 × 10⁻⁹ / 2.0 × 10⁻⁶ = 0.30, so θ ≈ 17.5°.

Question 22Main theoretical concepts fundamental to physics

A capacitor of capacitance 470 μF is charged to a potential difference of 10 V. What is the energy stored?

  1. 2.35 × 10⁻² J Correct answer.
  2. 4.7 × 10⁻³ J
  3. 9.4 × 10⁻² J
  4. 4.7 × 10⁻² J

Explanation

The energy stored in a capacitor is W = ½CV². Substituting gives ½ × 470 × 10⁻⁶ × 100 = 2.35 × 10⁻² J. The charge on the capacitor is 4.7 × 10⁻³ C, which is a different quantity with different units.

Question 23Main theoretical concepts fundamental to physics

A charged particle moves with velocity v perpendicular to a uniform magnetic field B. Which statement describes the subsequent motion?

  1. It moves in a straight line with increasing speed
  2. It moves in a helical path along the field direction
  3. It moves in a circular path of radius mv/(Bq) Correct answer.
  4. It remains stationary because the magnetic force is zero

Explanation

The magnetic force Bqv is always perpendicular to the velocity, so it does no work and the speed stays constant while the direction of motion changes continuously. The result is uniform circular motion with radius r = mv/(Bq). A helical path arises only when the velocity has a component along the field.

Question 24Main theoretical concepts fundamental to physics

Electromagnetic radiation is incident on a metal surface of work function 2.0 eV. Photons of energy 3.5 eV produce photoelectrons. What is the maximum kinetic energy of the emitted electrons?

  1. 3.5 eV
  2. 7.0 eV
  3. 1.5 eV Correct answer.
  4. 5.5 eV

Explanation

Einstein's photoelectric equation gives E_k(max) = hf − φ = 3.5 − 2.0 = 1.5 eV. The work function is the minimum energy needed to remove an electron, and the remainder appears as kinetic energy. Adding the two energies has no physical meaning in this context.

Question 25Main theoretical concepts fundamental to physics

A satellite orbits the Earth in a circular orbit. Which statement about its motion is correct?

  1. Its kinetic energy is greater in magnitude than its gravitational potential energy
  2. Its gravitational potential energy is positive and its total energy is positive
  3. Its total energy is negative and equals half its gravitational potential energy Correct answer.
  4. Its total energy is zero because it is in a bound orbit

Explanation

With the zero of potential energy at infinity, the gravitational potential energy of an orbiting body is negative and its magnitude is twice the kinetic energy. The total energy is therefore negative and equal to half the potential energy, which confirms that the satellite is bound.

Question 26Main theoretical concepts fundamental to physics

A student measures the diameter of a metal wire with a micrometer screw gauge and records 0.47 mm. The instrument has a zero error of +0.03 mm. What is the corrected diameter?

  1. 0.44 mm Correct answer.
  2. 0.50 mm
  3. 0.47 mm
  4. 0.40 mm

Explanation

A positive zero error means the instrument reads too large when the jaws are closed, so the error must be subtracted from every reading. Subtracting 0.03 mm from 0.47 mm gives 0.44 mm.

Question 27Main theoretical concepts fundamental to physics

Which pair of quantities are both scalar quantities in SI physics?

  1. Weight and momentum
  2. Mass and temperature Correct answer.
  3. Displacement and acceleration
  4. Force and velocity

Explanation

Scalars have magnitude only, and mass and thermodynamic temperature are both scalars with no direction. The other pairs each contain at least one vector quantity.

Question 28Main theoretical concepts fundamental to physics

A car travels 150 m due east and then 200 m due north. What is the magnitude of its resultant displacement?

  1. 350 m
  2. 50 m
  3. 250 m Correct answer.
  4. 175 m

Explanation

The two displacements are perpendicular, so the resultant is found with Pythagoras: the square root of (150² + 200²) equals the square root of 62 500, which is 250 m.

Question 29Main theoretical concepts fundamental to physics

An object is dropped from rest and falls freely under gravity, with air resistance negligible. Which quantity stays constant during the fall?

  1. Speed
  2. Distance travelled per second
  3. Acceleration Correct answer.
  4. Kinetic energy

Explanation

Near the Earth's surface free fall has a constant acceleration of about 9.81 m s⁻² downwards. Speed, kinetic energy and the distance covered each second all increase as the object falls.

Question 30Main theoretical concepts fundamental to physics

A force of 12 N acts on a body of mass 3.0 kg that moves in the direction of the force. What is the acceleration of the body?

  1. 4.0 m s⁻² Correct answer.
  2. 0.25 m s⁻²
  3. 36 m s⁻²
  4. 9.8 m s⁻²

Explanation

Newton's second law gives a = F/m, so 12 N divided by 3.0 kg is 4.0 m s⁻². The force and the motion are in the same direction, so no component resolution is needed.

Question 31Main theoretical concepts fundamental to physics

A stationary trolley of mass 2.0 kg is struck by a 1.0 kg ball moving at 6.0 m s⁻¹. The ball sticks to the trolley. What is the speed of the combined object immediately after the collision?

  1. 3.0 m s⁻¹
  2. 1.5 m s⁻¹
  3. 2.0 m s⁻¹ Correct answer.
  4. 6.0 m s⁻¹

Explanation

Momentum is conserved: 1.0 kg × 6.0 m s⁻¹ = 6.0 kg m s⁻¹ before, and the combined mass is 3.0 kg. Dividing gives a common speed of 2.0 m s⁻¹.

Question 32Main theoretical concepts fundamental to physics

An electric kettle rated at 2.0 kW is used for 3.0 minutes. How much electrical energy does it transfer?

  1. 1.1 × 10⁷ J
  2. 6.0 × 10³ J
  3. 3.6 × 10⁵ J Correct answer.
  4. 1.0 × 10² J

Explanation

Energy equals power multiplied by time, with the time converted to seconds: 2000 W × 180 s = 3.6 × 10⁵ J. Using minutes directly without conversion is the common error.

Question 33Main theoretical concepts fundamental to physics

Which statement about the strong nuclear force is correct?

  1. It acts only between protons and has infinite range.
  2. It acts between nucleons and is repulsive at very short range. Correct answer.
  3. It acts only between neutrons and is weaker than gravity.
  4. It acts between charged particles only and falls off as the inverse square of distance.

Explanation

The strong force binds nucleons together, being attractive at typical nuclear separations but strongly repulsive when nucleons are brought very close. It acts between all nucleons, not just charged ones.

Question 34Main theoretical concepts fundamental to physics

A block of weight 20 N rests on a rough horizontal surface. The coefficient of static friction is 0.40. What is the largest horizontal force that can be applied before the block starts to slide?

  1. 0.40 N
  2. 20 N
  3. 8.0 N Correct answer.
  4. 50 N

Explanation

The limiting static friction equals the coefficient of friction multiplied by the normal reaction, and on a horizontal surface the normal reaction equals the weight. So 0.40 × 20 N = 8.0 N.

Question 35Main theoretical concepts fundamental to physics

A projectile is launched at 30 m s⁻¹ at 40° above the horizontal on level ground, with air resistance negligible. Taking g = 9.8 m s⁻², what is the vertical component of its initial velocity?

  1. 23 m s⁻¹
  2. 25 m s⁻¹
  3. 19 m s⁻¹ Correct answer.
  4. 30 m s⁻¹

Explanation

The vertical component is v sin θ, so 30 × sin 40° ≈ 30 × 0.643 ≈ 19 m s⁻¹. The horizontal component would use cosine instead.

Question 36Main theoretical concepts fundamental to physics

A uniform metre rule is pivoted at its centre. A 2.0 N weight hangs 20 cm from the pivot on one side. Where must a 4.0 N weight be placed on the other side to balance the rule?

  1. 5.0 cm from the pivot
  2. 40 cm from the pivot
  3. 10 cm from the pivot Correct answer.
  4. 20 cm from the pivot

Explanation

For rotational equilibrium the moments must be equal: 2.0 N × 0.20 m = 0.40 N m. Dividing by 4.0 N gives 0.10 m, so the larger weight sits 10 cm from the pivot.

Question 37Main theoretical concepts fundamental to physics

A spring obeys Hooke's law with a spring constant of 250 N m⁻¹. It is compressed by 8.0 cm. What is the elastic potential energy stored?

  1. 0.80 J Correct answer.
  2. 0.080 J
  3. 1.6 J
  4. 20 J

Explanation

Elastic potential energy is ½kx², so 0.5 × 250 × (0.080)² = 0.5 × 250 × 0.0064 = 0.80 J. The extension must be in metres.

Question 38Main theoretical concepts fundamental to physics

A sound wave of frequency 500 Hz travels through air at 340 m s⁻¹. What is the separation between a compression and the adjacent rarefaction?

  1. 0.17 m
  2. 0.68 m
  3. 1.7 m
  4. 0.34 m Correct answer.

Explanation

The wavelength is v/f = 340/500 = 0.68 m. A compression and the next rarefaction are half a wavelength apart, so the separation is 0.34 m.

Question 39Main theoretical concepts fundamental to physics

A ray of light passes from air into glass of refractive index 1.5 at an angle of incidence of 30°. What is the angle of refraction?

  1. 20°
  2. 48°
  3. 30°
  4. 19° Correct answer.

Explanation

Snell's law gives n₁ sin θ₁ = n₂ sin θ₂, so sin θ₂ = sin 30°/1.5 = 0.333, and θ₂ ≈ 19°. The ray bends towards the normal because glass is optically denser.

Question 40Main theoretical concepts fundamental to physics

A 2.0 Ω resistor and a 6.0 Ω resistor are connected in series with a 12 V battery of negligible internal resistance. What is the potential difference across the 6.0 Ω resistor?

  1. 3.0 V
  2. 12 V
  3. 9.0 V Correct answer.
  4. 6.0 V

Explanation

The total resistance is 8.0 Ω, so the current is 12/8.0 = 1.5 A. The potential difference across 6.0 Ω is then 1.5 × 6.0 = 9.0 V, in proportion to the resistance.

Question 41Main theoretical concepts fundamental to physics

A 12 V battery with internal resistance 0.50 Ω is connected to an external resistor of 5.5 Ω. What is the terminal potential difference of the battery?

  1. 12 V
  2. 11 V Correct answer.
  3. 0.50 V
  4. 6.0 V

Explanation

The current is 12/(5.5 + 0.50) = 2.0 A. The lost volts across the internal resistance are 2.0 × 0.50 = 1.0 V, so the terminal potential difference is 12 − 1.0 = 11 V.

Question 42Main theoretical concepts fundamental to physics

A wire carries a current of 3.0 A perpendicular to a uniform magnetic field of flux density 0.20 T. The length of wire in the field is 0.50 m. What is the magnitude of the force on the wire?

  1. 0.10 N
  2. 3.0 N
  3. 0.30 N Correct answer.
  4. 1.2 N

Explanation

The force on a current-carrying conductor is F = BIL sin θ, and here θ = 90°, so 0.20 × 3.0 × 0.50 = 0.30 N.

Question 43Main theoretical concepts fundamental to physics

A capacitor of capacitance 220 μF is connected across a 6.0 V supply. What charge does it store?

  1. 1.3 × 10⁻³ C Correct answer.
  2. 3.7 × 10⁻⁵ C
  3. 2.2 × 10⁻⁴ C
  4. 1.3 × 10⁻⁶ C

Explanation

Charge equals capacitance multiplied by potential difference: 220 × 10⁻⁶ F × 6.0 V = 1.32 × 10⁻³ C, which rounds to 1.3 × 10⁻³ C.

Question 44Main theoretical concepts fundamental to physics

A transformer has 400 turns on its primary and 50 turns on its secondary. The primary is connected to a 240 V alternating supply. Assuming an ideal transformer, what is the secondary voltage?

  1. 120 V
  2. 1920 V
  3. 240 V
  4. 30 V Correct answer.

Explanation

For an ideal transformer the voltage ratio equals the turns ratio: V₂ = 240 × (50/400) = 30 V. A step-down turns ratio gives a step-down voltage.

Question 45Main theoretical concepts fundamental to physics

A monochromatic light source of wavelength 500 nm illuminates a double slit with a separation of 0.25 mm. The fringe spacing on a screen 2.0 m away is measured. What is the fringe spacing?

  1. 8.0 mm
  2. 4.0 mm Correct answer.
  3. 2.0 mm
  4. 0.50 mm

Explanation

Fringe spacing is λD/a, so (500 × 10⁻⁹ × 2.0)/(0.25 × 10⁻³) = 4.0 × 10⁻³ m, or 4.0 mm.

Question 46Main theoretical concepts fundamental to physics

The activity of a radioactive source falls from 800 Bq to 100 Bq in 36 hours. What is the half-life of the source?

  1. 24 hours
  2. 9.0 hours
  3. 12 hours Correct answer.
  4. 18 hours

Explanation

The activity falls by a factor of 8, which is 2³, so three half-lives have elapsed. Dividing 36 hours by 3 gives a half-life of 12 hours.

Question 47Main theoretical concepts fundamental to physics

An ideal gas undergoes an isothermal expansion. Which statement about the gas is correct?

  1. Its internal energy stays constant and it does work on its surroundings. Correct answer.
  2. Its temperature rises as its volume increases.
  3. Its pressure rises in proportion to its volume.
  4. No heat is exchanged with the surroundings.

Explanation

For an ideal gas the internal energy depends only on temperature, so an isothermal change keeps it constant. Since the gas expands, it does work, and it must absorb an equal amount of heat to keep the temperature fixed.

Question 48Main theoretical concepts fundamental to physics

A satellite in a circular orbit is moved to a higher circular orbit. Which statement about its motion is correct?

  1. Its orbital speed increases while its potential energy decreases.
  2. Its orbital speed and total energy both increase.
  3. Its orbital speed decreases while its total energy increases. Correct answer.
  4. Its orbital speed stays the same because gravity provides the centripetal force.

Explanation

Setting gravitational force equal to the centripetal requirement gives v² = GM/r, so a larger radius means a smaller orbital speed. The total energy becomes less negative because more work is done against gravity, so the total energy increases.

Question 49Main theoretical concepts fundamental to physics

A charged particle moves in a uniform electric field between two parallel plates. Which statement describes the path of the particle if it enters perpendicular to the field lines?

  1. A straight line along the field lines, because the force acts along the field.
  2. A parabola, because the force is constant and perpendicular to the initial velocity. Correct answer.
  3. A circle, because the electric force provides a constant central force.
  4. A straight line at constant speed, because the field does no work on the particle.

Explanation

The electric force qE is constant and perpendicular to the entry velocity, so it mimics projectile motion and the trajectory is parabolic. A circular path would need a force that always points towards a fixed centre.

Question 50Main theoretical concepts fundamental to physics

In a nuclear reaction, the total rest mass of the products is slightly less than that of the reactants. Which statement explains the energy released?

  1. The missing mass is converted into protons and neutrons.
  2. The mass defect appears as energy according to E = mc². Correct answer.
  3. The lost mass is stored as an increase in the binding energy of the nuclei.
  4. The energy released equals the mass defect multiplied by the charge.

Explanation

Einstein's mass-energy relation states that a decrease in rest mass Δm corresponds to released energy Δm c². The products are more tightly bound, so their total rest mass is smaller.