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HSC Physics practice questions

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Question 1Physics (Stage 6)

A car travels along a straight road at a constant speed of 20 m/s for 15 s, then decelerates uniformly to rest over 5 s. What is the total distance travelled?

  1. 250 m
  2. 350 m Correct answer.
  3. 400 m
  4. 300 m

Explanation

During the constant-speed phase the distance is speed times time, 20 × 15 = 300 m. During uniform deceleration the average speed is the mean of 20 m/s and 0, giving 10 m/s, so the extra distance is 10 × 5 = 50 m. Adding the two stages gives 350 m in total.

Question 2Physics (Stage 6)

A ball is projected horizontally from a table and lands on the floor. Neglecting air resistance, which statement about its motion is correct?

  1. The horizontal velocity decreases while the vertical velocity stays constant.
  2. The horizontal and vertical accelerations are both equal to g.
  3. Both the horizontal and vertical velocities increase uniformly with time.
  4. The horizontal velocity stays constant while the vertical velocity increases uniformly. Correct answer.

Explanation

With air resistance neglected, no horizontal force acts, so horizontal velocity is constant. The only force is weight, giving a constant downward acceleration g, so the vertical velocity grows uniformly from zero. The two components are independent, which is why the path is a parabola.

Question 3Physics (Stage 6)

A 1200 kg car rounds a flat circular curve of radius 50 m at a speed of 15 m/s. What is the minimum coefficient of static friction needed to keep the car on the curve? Take g = 9.8 m/s².

  1. 0.15
  2. 0.46 Correct answer.
  3. 0.30
  4. 0.92

Explanation

The required centripetal force is mv²/r, and friction provides it: μmg = mv²/r. Cancelling mass gives μ = v²/(rg) = 225/(50 × 9.8) ≈ 0.46. The mass of the car does not affect the answer because it cancels on both sides.

Question 4Physics (Stage 6)

Two satellites orbit Earth in circular orbits, one at radius r and one at radius 4r. What is the ratio of the orbital speed of the inner satellite to that of the outer satellite?

  1. 1 : 2
  2. 16 : 1
  3. 2 : 1 Correct answer.
  4. 4 : 1

Explanation

Gravitational force supplies the centripetal force, so GMm/r² = mv²/r, giving v = √(GM/r). Speed is therefore inversely proportional to the square root of the orbital radius. The ratio is √(4r/r) = 2, so the inner satellite moves twice as fast.

Question 5Physics (Stage 6)

A 0.50 kg ball moving at 8.0 m/s rebounds along the same line at 6.0 m/s. What is the magnitude of the impulse delivered to the ball?

  1. 7.0 N s Correct answer.
  2. 1.0 N s
  3. 4.0 N s
  4. 3.0 N s

Explanation

Impulse equals the change in momentum, and momentum is a vector. Taking the original direction as positive, Δp = m(v_final − v_initial) = 0.50(−6.0 − 8.0) = −7.0 kg m/s. The magnitude is therefore 7.0 N s.

Question 6Physics (Stage 6)

In a perfectly elastic collision between two objects, which quantity is conserved?

  1. Total momentum only
  2. Both total momentum and total kinetic energy Correct answer.
  3. Neither momentum nor kinetic energy
  4. Total kinetic energy only

Explanation

In any collision with no external net force, total momentum is conserved. In a perfectly elastic collision, kinetic energy is also conserved, which distinguishes it from inelastic collisions where kinetic energy is lost to other forms.

Question 7Physics (Stage 6)

A 2.0 kg mass hangs from a spring of spring constant 400 N/m. How far does the spring extend when the mass hangs at rest? Take g = 9.8 m/s².

  1. 0.20 m
  2. 0.049 m Correct answer.
  3. 4.9 m
  4. 0.98 m

Explanation

At equilibrium the spring force balances the weight, so kx = mg. Rearranging gives x = mg/k = (2.0 × 9.8)/400 = 0.049 m. The extension is independent of how the mass reaches equilibrium once it is at rest.

Question 8Physics (Stage 6)

A simple pendulum of length L has period T on Earth. What is its period on a planet where the acceleration due to gravity is four times that on Earth?

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

Explanation

The period of a simple pendulum is T = 2π√(L/g), so period is inversely proportional to the square root of g. Quadrupling g divides the period by √4 = 2. The mass of the bob plays no role in this result.

Question 9Physics (Stage 6)

A wave has a frequency of 250 Hz and a wavelength of 1.4 m. What is its speed?

  1. 180 m/s
  2. 1.4 m/s
  3. 250 m/s
  4. 350 m/s Correct answer.

Explanation

The wave equation relates speed, frequency and wavelength by v = fλ. Substituting gives v = 250 × 1.4 = 350 m/s. Frequency and wavelength are independent properties fixed by the source and the medium.

Question 10Physics (Stage 6)

Two coherent light sources produce an interference pattern on a screen. Which condition produces a dark fringe at a point?

  1. The path difference from the two sources is a whole multiple of the wavelength.
  2. The path difference from the two sources is an odd multiple of half a wavelength. Correct answer.
  3. The light from the two sources has different frequencies.
  4. The light from the two sources is polarised in perpendicular planes.

Explanation

Destructive interference occurs when waves arrive in antiphase, which happens when the path difference is a half-integer multiple of the wavelength. The waves then cancel, producing a minimum in intensity. Whole-multiple path differences give constructive interference instead.

Question 11Physics (Stage 6)

A standing wave is formed on a string fixed at both ends. The distance between two adjacent nodes is 0.25 m. What is the wavelength of the wave on the string?

  1. 0.125 m
  2. 0.25 m
  3. 1.0 m
  4. 0.50 m Correct answer.

Explanation

In a standing wave, adjacent nodes are separated by half a wavelength. If that separation is 0.25 m, then the wavelength is twice this value, 0.50 m. This spacing is the same for every harmonic.

Question 12Physics (Stage 6)

Which statement correctly describes the refraction of light passing from air into glass?

  1. The light bends towards the normal because its frequency increases in glass.
  2. The light bends away from the normal because it speeds up in the denser medium.
  3. The light bends towards the normal because it slows down in the denser medium. Correct answer.
  4. The light continues straight because frequency changes at the boundary.

Explanation

Glass has a higher refractive index than air, so light travels more slowly in glass. According to Snell's law, a decrease in speed at the boundary bends the ray towards the normal. The frequency stays constant across the boundary; only speed and wavelength change.

Question 13Physics (Stage 6)

A resistor of 12 Ω is connected in series with a parallel combination of two 6 Ω resistors. What is the total resistance of the circuit?

  1. 18 Ω
  2. 24 Ω
  3. 15 Ω Correct answer.
  4. 9 Ω

Explanation

Two equal 6 Ω resistors in parallel have an equivalent resistance of 3 Ω, since 1/R = 1/6 + 1/6. Adding the series 12 Ω resistor gives 12 + 3 = 15 Ω. Resistances in series add directly.

Question 14Physics (Stage 6)

A wire of length 0.40 m carries a current of 3.0 A perpendicular to a uniform magnetic field of 0.50 T. What is the magnitude of the force on the wire?

  1. 1.5 N
  2. 6.0 N
  3. 0.060 N
  4. 0.60 N Correct answer.

Explanation

The magnetic force on a current-carrying wire is F = BIL sin θ. With the wire perpendicular to the field, sin θ = 1, so F = 0.50 × 3.0 × 0.40 = 0.60 N. The direction is given by the right-hand palm rule.

Question 15Physics (Stage 6)

A transformer has 400 turns on its primary coil and 50 turns on its secondary coil. If the primary is supplied with 240 V alternating voltage, what is the secondary voltage, assuming ideal conditions?

  1. 1920 V
  2. 60 V
  3. 30 V Correct answer.
  4. 120 V

Explanation

For an ideal transformer the voltage ratio equals the turns ratio: Vs/Vp = Ns/Np. Here Vs = 240 × (50/400) = 30 V, a step-down result consistent with fewer secondary turns. An ideal transformer conserves power, so the secondary current is correspondingly larger.

Question 16Physics (Stage 6)

Electromagnetic induction produces an induced emf in a coil when which condition is satisfied?

  1. The coil is made of insulating material
  2. The magnetic flux through the coil changes with time Correct answer.
  3. The coil carries a steady current
  4. The coil is at rest in a uniform magnetic field

Explanation

Faraday's law states that the induced emf equals the negative rate of change of magnetic flux through the circuit. A steady situation, such as a stationary coil in a uniform field, gives zero induced emf. Only a change in flux, whether from motion or a varying field, induces an emf.

Question 17Physics (Stage 6)

In the photoelectric effect, light of frequency f is shone on a metal surface with work function W. What is the maximum kinetic energy of the emitted electrons?

  1. W − hf
  2. hf − W Correct answer.
  3. hf / W
  4. hf + W

Explanation

Einstein's photoelectric equation gives the maximum kinetic energy as the photon energy minus the work function: K_max = hf − W. The work function is the minimum energy needed to release an electron from the metal. Any excess photon energy appears as kinetic energy of the electron.

Question 18Physics (Stage 6)

An electron is accelerated through a potential difference of 500 V. What is its kinetic energy in electron-volts?

  1. 500 J
  2. 500 eV Correct answer.
  3. 1.6 × 10⁻¹⁹ eV
  4. 8.0 × 10⁻¹⁷ eV

Explanation

By definition, one electron-volt is the energy gained by an electron accelerated through one volt. Therefore an electron accelerated through 500 V gains 500 eV of kinetic energy. Converting to joules would multiply by 1.6 × 10⁻¹⁹.

Question 19Physics (Stage 6)

A nucleus of uranium-238 emits an alpha particle. What are the mass number and atomic number of the resulting nucleus?

  1. 234 and 90 Correct answer.
  2. 236 and 92
  3. 234 and 92
  4. 238 and 90

Explanation

An alpha particle is a helium nucleus with mass number 4 and atomic number 2. Alpha decay therefore reduces the mass number by 4 and the atomic number by 2, giving 234 and 90. This is the nucleus of thorium-234.

Question 20Physics (Stage 6)

A sample contains a radioactive isotope with a half-life of 8 days. What fraction of the original nuclei remains after 24 days?

  1. 1/24
  2. 1/8 Correct answer.
  3. 1/6
  4. 1/3

Explanation

The number of half-lives elapsed is 24 ÷ 8 = 3. Each half-life halves the remaining nuclei, so the fraction left is (1/2)³ = 1/8. Half-life is a statistical property of the isotope and does not depend on the sample size.

Question 21Physics (Stage 6)

Which statement best describes the strong nuclear force?

  1. It is attractive between nucleons at short range and overcomes electrostatic repulsion in the nucleus. Correct answer.
  2. It repels nucleons from each other at very short range and at all longer ranges.
  3. It is weaker than gravity at nuclear distances.
  4. It acts only between protons and has a range larger than the whole atom.

Explanation

The strong force binds protons and neutrons together and is attractive over a very short range of about a femtometre. It is much stronger than the electrostatic repulsion between protons at these distances, which is why nuclei are stable. Beyond nuclear distances it falls rapidly to negligible strength.

Question 22Physics (Stage 6)

A rocket in deep space fires its engine so that its speed increases. Which statement about its mass and energy is consistent with special relativity?

  1. Its rest mass decreases as its speed increases.
  2. Its kinetic energy increases without limit as its speed approaches c.
  3. Its relativistic mass-equivalent energy increases as its kinetic energy increases. Correct answer.
  4. Its total energy remains constant regardless of speed.

Explanation

In special relativity the total energy of a particle is E = γmc², so energy increases with speed. The rest mass m is invariant and does not change with motion. The kinetic energy approaches infinity only as speed approaches c, which no massive object can reach.

Question 23Physics (Stage 6)

A projectile is launched at 30 m/s at 40° above the horizontal on level ground. Neglecting air resistance, what is the horizontal component of its velocity at the highest point of its path? Take cos 40° = 0.766.

  1. 19 m/s
  2. 30 m/s
  3. 0 m/s
  4. 23 m/s Correct answer.

Explanation

The horizontal velocity component v cos θ remains constant throughout the flight because no horizontal force acts. At the highest point only the vertical component is zero, so the horizontal component is still 30 × 0.766 ≈ 23 m/s. Substituting zero for the whole velocity at the top is a common error.

Question 24Physics (Stage 6)

A 0.20 kg mass on a spring oscillates with amplitude 0.10 m and angular frequency 5.0 rad/s. What is the maximum kinetic energy of the mass?

  1. 0.025 J Correct answer.
  2. 0.050 J
  3. 0.50 J
  4. 0.010 J

Explanation

In simple harmonic motion the maximum speed is v_max = Aω = 0.10 × 5.0 = 0.50 m/s. The maximum kinetic energy is ½mv² = ½ × 0.20 × 0.25 = 0.025 J. This equals the total energy of the oscillator, which is also ½kA².

Question 25Physics (Stage 6)

A 2.0 kg block slides down a frictionless incline of height 5.0 m and then compresses a spring at the bottom. If the spring constant is 500 N/m, what is the maximum compression? Take g = 9.8 m/s².

  1. 1.4 m
  2. 0.44 m
  3. 0.20 m
  4. 0.63 m Correct answer.

Explanation

Conservation of energy equates the gravitational potential energy lost to the elastic energy stored: mgh = ½kx². So x = √(2mgh/k) = √(2 × 2.0 × 9.8 × 5.0 / 500) ≈ 0.63 m. The incline angle does not matter because the incline is frictionless.

Question 26Physics (Stage 6)

A car travels 150 m due east in 10 s, then 150 m due west in 15 s. What is the magnitude of its average velocity for the whole journey?

  1. 6.0 m/s
  2. 15.0 m/s
  3. 12.0 m/s
  4. 0 m/s Correct answer.

Explanation

Average velocity is total displacement divided by total time. The eastward and westward displacements cancel, giving zero total displacement, so the average velocity is zero even though the car moved.

Question 27Physics (Stage 6)

A ball is dropped from rest and falls freely for 3.0 s. Taking g = 9.8 m/s², how far has it fallen?

  1. 14.7 m
  2. 44.1 m Correct answer.
  3. 29.4 m
  4. 88.2 m

Explanation

For motion from rest under constant acceleration, displacement equals ½at². Substituting a = 9.8 m/s² and t = 3.0 s gives ½ × 9.8 × 9 = 44.1 m.

Question 28Physics (Stage 6)

A box sits at rest on a rough horizontal floor. Which statement correctly describes the forces acting on the box?

  1. The weight and normal force are equal and opposite, and friction is zero. Correct answer.
  2. The normal force is greater than the weight because the floor is rough.
  3. Friction acts horizontally while the normal force acts along the weight.
  4. The normal force is less than the weight because friction supports part of it.

Explanation

With no applied horizontal force and no acceleration, the vertical forces balance so the normal force equals the weight. Static friction only arises to oppose an applied tendency to slide, so it is zero here.

Question 29Physics (Stage 6)

A 1200 kg car rounds a flat curve of radius 50 m at 15 m/s. What is the magnitude of the centripetal force required?

  1. 5400 N Correct answer.
  2. 240 N
  3. 360 N
  4. 18000 N

Explanation

Centripetal force equals mv²/r. Substituting m = 1200 kg, v = 15 m/s and r = 50 m gives 1200 × 225 ÷ 50 = 5400 N, supplied here by friction between tyres and road.

Question 30Physics (Stage 6)

Two satellites orbit Earth at different radii. Which statement about their motion is correct?

  1. Both satellites have the same orbital speed because gravity is the same.
  2. The satellite at the larger radius has the smaller orbital speed. Correct answer.
  3. Orbital speed is independent of the mass of Earth.
  4. The satellite at the larger radius has the shorter orbital period.

Explanation

For a circular orbit, gravitational force provides the centripetal force, giving v = √(GM/r). Speed therefore decreases as orbital radius increases, and the larger-radius satellite moves more slowly and takes longer per orbit.

Question 31Physics (Stage 6)

A 0.50 kg ball moving at 8.0 m/s strikes a wall and rebounds along the same line at 6.0 m/s. What is the magnitude of its change in momentum?

  1. 7.0 kg m/s Correct answer.
  2. 3.0 kg m/s
  3. 4.0 kg m/s
  4. 1.0 kg m/s

Explanation

Momentum is a vector, so the reversal of direction must be included. Taking the initial direction as positive, the change is 0.50 × (−6.0) − 0.50 × 8.0 = −7.0 kg m/s, with magnitude 7.0 kg m/s.

Question 32Physics (Stage 6)

A force of 20 N acts on a body and does 100 J of work. At what angle to the displacement is the force applied if the body moves 10 m?

  1. 45°
  2. 60° Correct answer.
  3. 90°
  4. 0°

Explanation

Work equals Fd cos θ. Here cos θ = 100 ÷ (20 × 10) = 0.5, so θ = 60°, meaning only the component of force along the displacement does work.

Question 33Physics (Stage 6)

A spring stores 4.0 J of elastic potential energy when compressed by 0.20 m. What is its spring constant?

  1. 20 N/m
  2. 100 N/m
  3. 200 N/m Correct answer.
  4. 40 N/m

Explanation

Elastic potential energy equals ½kx². Rearranging gives k = 2E/x² = 2 × 4.0 ÷ 0.04 = 200 N/m, showing the strong dependence on compression.

Question 34Physics (Stage 6)

A student measures the period of a pendulum ten times and averages the results. Which statement best explains why this improves reliability?

  1. Averaging reduces the effect of random timing variations. Correct answer.
  2. Averaging changes the physical period of the pendulum.
  3. Averaging increases the accuracy of the length measurement.
  4. Averaging removes systematic error from the timing device.

Explanation

Repeated measurements scatter randomly about a mean, and averaging reduces the influence of random fluctuations. Systematic errors, such as a zero error in a stopwatch, are unaffected by averaging.

Question 35Physics (Stage 6)

A sound wave travels from air into water, where its speed is greater. What happens to its frequency and wavelength?

  1. Frequency increases and wavelength stays the same.
  2. Frequency stays the same and wavelength decreases.
  3. Frequency stays the same and wavelength increases. Correct answer.
  4. Both frequency and wavelength increase.

Explanation

Frequency is set by the source and does not change at a boundary. Since v = fλ and the speed rises while frequency is fixed, the wavelength must increase.

Question 36Physics (Stage 6)

A police siren emits sound at 800 Hz. The car approaches a stationary observer at 20 m/s while the speed of sound is 340 m/s. What frequency is heard?

  1. 753 Hz
  2. 800 Hz
  3. 850 Hz Correct answer.
  4. 640 Hz

Explanation

For a source approaching a stationary observer, the observed frequency is f × v/(v − vs). Substituting gives 800 × 340/320 = 850 Hz, a higher pitch caused by compressed wavefronts.

Question 37Physics (Stage 6)

Two identical resistors are connected in parallel across a battery. How does the total power dissipated compare with one resistor alone across the same battery?

  1. It is doubled. Correct answer.
  2. It is quadrupled.
  3. It is halved.
  4. It is unchanged.

Explanation

In parallel, each resistor receives the full battery voltage, so each dissipates V²/R and the total is 2V²/R. The total power is therefore twice that of a single resistor.

Question 38Physics (Stage 6)

A 6.0 V battery with internal resistance 1.0 Ω is connected to a 5.0 Ω resistor. What is the terminal voltage of the battery?

  1. 4.0 V
  2. 1.0 V
  3. 6.0 V
  4. 5.0 V Correct answer.

Explanation

The current is emf divided by total resistance, 6.0 ÷ 6.0 = 1.0 A. The terminal voltage is emf minus the internal drop, 6.0 − 1.0 × 1.0 = 5.0 V.

Question 39Physics (Stage 6)

A charged particle moves in a uniform magnetic field with its velocity parallel to the field lines. What is the magnetic force on it?

  1. Equal to qvB
  2. Maximum, directed opposite the field
  3. Maximum, directed along the field
  4. Zero Correct answer.

Explanation

The magnetic force is qvB sin θ, where θ is the angle between velocity and field. When the velocity is parallel, θ = 0 and sin θ = 0, so no magnetic force acts on the particle.

Question 40Physics (Stage 6)

A coil of 200 turns and area 0.010 m² lies in a magnetic field that increases uniformly from 0 to 0.50 T in 0.20 s. What is the magnitude of the induced emf?

  1. 1.0 V
  2. 50 V
  3. 5.0 V Correct answer.
  4. 0.50 V

Explanation

Faraday's law gives emf = N × ΔΦ/Δt, with flux change ΔBA = 0.50 × 0.010 = 5.0 × 10⁻³ Wb. Then emf = 200 × 5.0 × 10⁻³ ÷ 0.20 = 5.0 V.

Question 41Physics (Stage 6)

In a step-up transformer assumed ideal, the secondary voltage is higher than the primary voltage. Which statement is correct?

  1. The secondary current is also higher than the primary current.
  2. The frequency of the output is higher than the input.
  3. The power output exceeds the power input.
  4. The secondary current is lower than the primary current. Correct answer.

Explanation

An ideal transformer conserves power, so VpIp = VsIs. If the secondary voltage is larger, the secondary current must be proportionally smaller, keeping power constant.

Question 42Physics (Stage 6)

A metal surface has a threshold frequency of 5.0 × 10¹⁴ Hz. Light of frequency 8.0 × 10¹⁴ Hz is incident on it. What is the maximum kinetic energy of the emitted electrons? Use h = 6.63 × 10⁻³⁴ J s.

  1. 3.3 × 10⁻¹⁹ J
  2. 1.99 × 10⁻¹⁹ J Correct answer.
  3. 2.0 × 10⁻¹⁹ J
  4. 5.3 × 10⁻¹⁹ J

Explanation

Einstein's photoelectric equation gives maximum kinetic energy as h(f − f₀). The frequency difference is 3.0 × 10¹⁴ Hz, so the energy is 6.63 × 10⁻³⁴ × 3.0 × 10¹⁴ ≈ 1.99 × 10⁻¹⁹ J.

Question 43Physics (Stage 6)

An electron in a hydrogen atom falls from the n = 3 level to the n = 2 level. What happens to the atom and the emitted photon?

  1. The atom gains energy and absorbs a photon of fixed energy.
  2. The atom loses energy and absorbs a photon of the same energy.
  3. The atom loses energy and emits a photon whose energy equals the level difference. Correct answer.
  4. The atom gains energy and emits a photon of fixed energy.

Explanation

A transition to a lower energy level releases energy, carried away by a single photon. The photon energy equals the difference between the two energy levels, giving a discrete spectral line.

Question 44Physics (Stage 6)

A radioactive source has an activity of 800 Bq. After 36 days the activity is 100 Bq. What is the half-life of the source?

  1. 6 days
  2. 18 days
  3. 12 days Correct answer.
  4. 9 days

Explanation

The activity falls from 800 to 100 Bq, a factor of eight, which corresponds to three half-lives. Three half-lives occupy 36 days, so each half-life is 12 days.

Question 45Physics (Stage 6)

In a nuclear fission reaction, the total mass of the products is slightly less than the mass of the reactants. What does this mass difference represent?

  1. Mass converted into additional protons
  2. Mass lost because neutrons escape the reactor
  3. Mass converted to energy released in the reaction Correct answer.
  4. Experimental error in the mass measurement

Explanation

The mass defect is related to the released energy by E = mc². The missing mass appears as kinetic energy of the fission fragments and radiation, which is how a reactor generates power.

Question 46Physics (Stage 6)

A student measures g by timing a falling object and obtains 9.2 m/s². The accepted value is 9.8 m/s². Which statement best describes the result?

  1. It is precise but not accurate. Correct answer.
  2. It is both accurate and precise.
  3. It is neither accurate nor precise.
  4. It is accurate but not precise.

Explanation

Accuracy refers to closeness to the accepted value, while precision refers to the spread of repeated measurements. A result systematically below 9.8 m/s² is inaccurate, but repeated trials could still cluster tightly and so be precise.

Question 47Physics (Stage 6)

A 2.0 kg trolley moving at 3.0 m/s collides with and sticks to a stationary 1.0 kg trolley. What is their common velocity after the collision?

  1. 3.0 m/s
  2. 2.0 m/s Correct answer.
  3. 1.0 m/s
  4. 1.5 m/s

Explanation

In a perfectly inelastic collision, momentum is conserved: 2.0 × 3.0 = (2.0 + 1.0) × v. Solving gives v = 6.0 ÷ 3.0 = 2.0 m/s, and kinetic energy is lost in the process.

Question 48Physics (Stage 6)

A projectile is launched horizontally from a cliff and another is dropped from the same height at the same instant. Neglecting air resistance, which reaches the ground first?

  1. The dropped projectile
  2. It depends on the launch speed
  3. Both reach the ground at the same time Correct answer.
  4. The horizontally launched projectile

Explanation

Horizontal and vertical motions are independent. Both projectiles start with zero vertical velocity and fall the same vertical distance under gravity, so their times of flight are equal regardless of horizontal speed.

Question 49Physics (Stage 6)

A wave is described by the equation y = 0.05 sin(4πt − 2πx), with SI units. What is the speed of the wave?

  1. 2.0 m/s Correct answer.
  2. 0.5 m/s
  3. 4.0 m/s
  4. 8.0 m/s

Explanation

Comparing with y = A sin(ωt − kx) gives ω = 4π rad/s and k = 2π rad/m. Wave speed is ω/k = 4π ÷ 2π = 2.0 m/s, with the wave travelling in the positive x direction.

Question 50Physics (Stage 6)

A light ray strikes a glass block at the critical angle. Which statement describes the refracted ray at that angle?

  1. It passes into the second medium at 90° to the normal.
  2. It is completely absorbed at the surface.
  3. It travels along the boundary between the two media. Correct answer.
  4. It is reflected straight back along the incident path.

Explanation

At the critical angle the angle of refraction in the less dense medium is 90°, so the refracted ray grazes along the boundary. Beyond this angle total internal reflection occurs and no light is transmitted.