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Saga Public High School Entrance Examination - Science study materials
Saga Public High School Entrance Examination - Science study resources

Saga Public High School Entrance Examination - Science practice questions

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Question 1Physics: mechanics, forces, energy, electricity and magnetism, waves

A cyclist travels 120 m east in 20 s, then 80 m west in 20 s. What is the magnitude of the average velocity for the whole trip?

  1. 5.0 m/s
  2. 2.0 m/s
  3. 1.0 m/s Correct answer.
  4. 4.0 m/s

Explanation

Average velocity uses total displacement divided by total time. The net displacement is 120 m − 80 m = 40 m east over 40 s, giving 1.0 m/s. Average speed would instead use the total path length of 200 m.

Question 2Physics: mechanics, forces, energy, electricity and magnetism, waves

A ball is dropped from rest and falls freely near Earth's surface, where g = 9.8 m/s². Ignoring air resistance, how far has it fallen after 3.0 s?

  1. 29.4 m
  2. 9.8 m
  3. 88.2 m
  4. 44.1 m Correct answer.

Explanation

For free fall from rest, distance s = ½gt². Substituting gives ½ × 9.8 × 9.0 = 44.1 m. The velocity after 3.0 s is 29.4 m/s, but that is a speed, not a distance.

Question 3Physics: mechanics, forces, energy, electricity and magnetism, waves

A box is pushed across a rough horizontal floor at constant velocity by a horizontal force of 40 N. What is the magnitude of the kinetic friction force acting on the box?

  1. Less than 40 N but greater than 0 N
  2. 40 N Correct answer.
  3. More than 40 N
  4. 0 N

Explanation

Constant velocity means the net horizontal force is zero, so the applied force and kinetic friction must balance exactly. Friction therefore equals 40 N in magnitude and points opposite to the motion.

Question 4Physics: mechanics, forces, energy, electricity and magnetism, waves

Which quantity is a scalar?

  1. Kinetic energy Correct answer.
  2. Acceleration
  3. Displacement
  4. Force

Explanation

A scalar is fully described by magnitude alone, and kinetic energy has no direction. Displacement, acceleration and force are all vectors because each requires a direction as well as a size.

Question 5Physics: mechanics, forces, energy, electricity and magnetism, waves

A 2.0 kg object moving at 3.0 m/s collides head-on with a stationary 1.0 kg object, and they stick together. What is the speed of the combined object just after the collision?

  1. 2.0 m/s Correct answer.
  2. 1.5 m/s
  3. 0.5 m/s
  4. 3.0 m/s

Explanation

Momentum is conserved in the collision: 2.0 × 3.0 = (2.0 + 1.0) × v. Solving gives v = 6.0 ÷ 3.0 = 2.0 m/s. Kinetic energy is not conserved because the collision is perfectly inelastic.

Question 6Physics: mechanics, forces, energy, electricity and magnetism, waves

A 500 N crate is lifted vertically at constant speed through 2.0 m in 4.0 s. What average power is delivered to the crate?

  1. 4000 W
  2. 250 W Correct answer.
  3. 1000 W
  4. 62.5 W

Explanation

Power is work done per unit time, and the work against gravity is force times distance: 500 N × 2.0 m = 1000 J. Dividing by 4.0 s gives 250 W.

Question 7Physics: mechanics, forces, energy, electricity and magnetism, waves

A pendulum bob swings from its highest point to its lowest point. Assuming negligible air resistance, which statement about its energy is correct?

  1. Kinetic energy is greatest at the highest point.
  2. Gravitational potential energy is greatest at the lowest point.
  3. Gravitational potential energy is converted into kinetic energy as it descends. Correct answer.
  4. Total mechanical energy decreases as it descends.

Explanation

As the bob falls, its height decreases so gravitational potential energy falls, and its speed increases so kinetic energy rises. With negligible air resistance the total mechanical energy stays constant during the swing.

Question 8Physics: mechanics, forces, energy, electricity and magnetism, waves

A uniform metre rule is pivoted at its centre. A 2.0 N weight hangs 20 cm to the left of the pivot. Where must a 4.0 N weight be hung to balance the rule?

  1. 40 cm to the right of the pivot
  2. 10 cm to the right of the pivot Correct answer.
  3. 20 cm to the right of the pivot
  4. 5 cm to the right of the pivot

Explanation

For rotational balance the moments about the pivot must be equal: 2.0 N × 20 cm = 40 N·cm. The 4.0 N weight must therefore sit at 40 ÷ 4.0 = 10 cm from the pivot on the opposite side.

Question 9Physics: mechanics, forces, energy, electricity and magnetism, waves

A wave has a frequency of 50 Hz and a wavelength of 0.40 m. What is its speed?

  1. 0.008 m/s
  2. 125 m/s
  3. 20 m/s Correct answer.
  4. 50.4 m/s

Explanation

Wave speed equals frequency multiplied by wavelength: v = fλ. Here 50 Hz × 0.40 m = 20 m/s. Frequency is the number of cycles per second and wavelength is the distance per cycle.

Question 10Physics: mechanics, forces, energy, electricity and magnetism, waves

A ray of light passes from air into glass and bends towards the normal. Which statement explains this?

  1. Light travels faster in glass than in air.
  2. The frequency of the light increases in glass.
  3. The wavelength of the light increases in glass.
  4. Light travels more slowly in glass than in air. Correct answer.

Explanation

Glass is optically denser than air, so light travels more slowly in it. The change in speed at the boundary causes the ray to change direction, bending towards the normal when entering the denser medium.

Question 11Physics: mechanics, forces, energy, electricity and magnetism, waves

A 12 V battery is connected across a 6.0 Ω resistor. What current flows through the resistor?

  1. 2.0 A Correct answer.
  2. 18 A
  3. 72 A
  4. 0.5 A

Explanation

Ohm's law states that current equals voltage divided by resistance: I = V/R. Substituting gives 12 V ÷ 6.0 Ω = 2.0 A.

Question 12Physics: mechanics, forces, energy, electricity and magnetism, waves

Two identical resistors are connected in parallel across a battery. Compared with a single resistor connected alone across the same battery, the total resistance of the parallel pair is:

  1. twice as large
  2. half as large Correct answer.
  3. the same
  4. four times as large

Explanation

For two equal resistors in parallel, the combined resistance is the single value divided by two. Adding a parallel path gives the current more routes, so total resistance falls.

Question 13Physics: mechanics, forces, energy, electricity and magnetism, waves

An electric heater carries a current of 4.0 A when connected to a 230 V supply. What is its power rating?

  1. 3680 W
  2. 920 W Correct answer.
  3. 234 W
  4. 57.5 W

Explanation

Electrical power is the product of voltage and current: P = VI. Here 230 V × 4.0 A = 920 W. The resistance would be 230 ÷ 4.0 = 57.5 Ω, which is a resistance, not a power.

Question 14Physics: mechanics, forces, energy, electricity and magnetism, waves

A straight wire carrying a current is placed between the poles of a magnet so that the current is perpendicular to the magnetic field. Which change increases the magnitude of the force on the wire?

  1. Removing the magnetic field
  2. Aligning the wire parallel to the field
  3. Increasing the current in the wire Correct answer.
  4. Reversing the direction of the current

Explanation

The force on a current-carrying wire in a magnetic field is proportional to the current, the field strength and the length in the field. Increasing the current therefore increases the force. Reversing the current only reverses the direction of the force.

Question 15Physics: mechanics, forces, energy, electricity and magnetism, waves

A step-down transformer has 1000 turns on its primary coil and 200 turns on its secondary coil. If the primary voltage is 240 V, what is the secondary voltage?

  1. 1200 V
  2. 24 V
  3. 240 V
  4. 48 V Correct answer.

Explanation

For an ideal transformer the voltage ratio equals the turns ratio: Vs/Vp = Ns/Np. Thus Vs = 240 × (200/1000) = 48 V. A step-down transformer reduces voltage because the secondary has fewer turns.

Question 16Physics: mechanics, forces, energy, electricity and magnetism, waves

A student measures the extension of a spring for several hanging masses and plots extension against load. The graph is a straight line through the origin until a point beyond which it curves. What does the straight section represent?

  1. The spring constant increases as the load increases.
  2. The spring is no longer able to return to its original length.
  3. The spring obeys Hooke's law, with extension proportional to load. Correct answer.
  4. The spring has reached its elastic limit.

Explanation

A straight line through the origin shows that extension is directly proportional to the applied load, which is the statement of Hooke's law. The gradient of this line equals 1/k, where k is the spring constant.

Question 17Physics: mechanics, forces, energy, electricity and magnetism, waves

A car accelerates uniformly from 5.0 m/s to 25 m/s in 8.0 s. What is its acceleration?

  1. 0.40 m/s²
  2. 3.75 m/s²
  3. 2.5 m/s² Correct answer.
  4. 30 m/s²

Explanation

Acceleration is the change in velocity divided by the time taken: a = (25 − 5.0) ÷ 8.0. This gives 20 ÷ 8.0 = 2.5 m/s².

Question 18Physics: mechanics, forces, energy, electricity and magnetism, waves

A 10 kg block rests on a horizontal surface. The coefficient of static friction between the block and the surface is 0.40. Taking g = 10 m/s², what is the minimum horizontal force needed to start the block moving?

  1. 40 N Correct answer.
  2. 100 N
  3. 4 N
  4. 25 N

Explanation

The normal force on a horizontal surface equals the weight, 10 kg × 10 m/s² = 100 N. The maximum static friction is 0.40 × 100 N = 40 N, so a force just above 40 N is needed to start motion.

Question 19Physics: mechanics, forces, energy, electricity and magnetism, waves

A sound wave travels through air at 340 m/s. A source emits a note of frequency 170 Hz. What is the wavelength of the sound?

  1. 57800 m
  2. 2.0 m Correct answer.
  3. 0.5 m
  4. 510 m

Explanation

Rearranging v = fλ gives λ = v/f. Substituting 340 m/s ÷ 170 Hz = 2.0 m. The wavelength is the distance the wave advances in one complete cycle.

Question 20Physics: mechanics, forces, energy, electricity and magnetism, waves

A 0.50 kg ball moving at 8.0 m/s is brought to rest by a constant force in 0.20 s. What is the magnitude of the average force?

  1. 20 N Correct answer.
  2. 0.80 N
  3. 40 N
  4. 4.0 N

Explanation

The change in momentum is 0.50 kg × 8.0 m/s = 4.0 kg·m/s. Using force equals change in momentum divided by time gives 4.0 ÷ 0.20 = 20 N.

Question 21Physics: mechanics, forces, energy, electricity and magnetism, waves

A 60 W lamp and a 100 W lamp, both designed for the same mains voltage, are connected in series across that voltage. Which lamp glows more brightly and why?

  1. The 100 W lamp, because it has the higher power rating.
  2. The 60 W lamp, because it has the greater resistance and dissipates more power in series. Correct answer.
  3. Both glow equally because the same current passes through them.
  4. Neither glows, because lamps in series cannot operate.

Explanation

The 60 W lamp has the higher resistance since R = V²/P. In series both carry the same current, and power dissipated is I²R, so the larger resistance dissipates more power and glows brighter.

Question 22Physics: mechanics, forces, energy, electricity and magnetism, waves

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

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

Explanation

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

Question 23Physics: mechanics, forces, energy, electricity and magnetism, waves

A block slides down a frictionless incline of height 1.8 m from rest. Taking g = 10 m/s², what is its speed at the bottom?

  1. 36 m/s
  2. 6.0 m/s Correct answer.
  3. 18 m/s
  4. 3.0 m/s

Explanation

On a frictionless incline, gravitational potential energy converts fully to kinetic energy: mgh = ½mv². Cancelling mass gives v = √(2gh) = √(2 × 10 × 1.8) = √36 = 6.0 m/s.

Question 24Physics: mechanics, forces, energy, electricity and magnetism, waves

Three identical resistors, each of resistance R, are connected in parallel. What single resistance is equivalent to the combination?

  1. 3R
  2. R
  3. R/3 Correct answer.
  4. R/9

Explanation

For n identical resistors in parallel, the equivalent resistance is R divided by n. With three equal resistors, 1/Req = 3/R, so Req = R/3.

Question 25Physics: mechanics, forces, energy, electricity and magnetism, waves

A transverse wave on a string has an amplitude of 0.10 m and a wavelength of 2.0 m. The wave travels at 8.0 m/s. What is the frequency of the wave?

  1. 16 Hz
  2. 0.25 Hz
  3. 4.0 Hz Correct answer.
  4. 0.05 Hz

Explanation

Frequency is wave speed divided by wavelength: f = v/λ. Substituting gives 8.0 m/s ÷ 2.0 m = 4.0 Hz. The amplitude affects the size of the disturbance, not the frequency.

Question 26Physics: mechanics, forces, energy, electricity and magnetism, waves

A student walks 3.0 km due east and then 4.0 km due north. What is the magnitude of the student's resultant displacement from the starting point?

  1. 1.0 km
  2. 3.5 km
  3. 5.0 km Correct answer.
  4. 7.0 km

Explanation

The two legs are perpendicular, so the resultant displacement is the hypotenuse of a right triangle: √(3.0² + 4.0²) = √25 = 5.0 km. Adding the distances gives total path length, not displacement.

Question 27Physics: mechanics, forces, energy, electricity and magnetism, waves

A cyclist moves along a straight road at a constant velocity of 6.0 m/s for 25 s. What distance does the cyclist travel in this time?

  1. 150 m Correct answer.
  2. 31 m
  3. 0.24 m
  4. 4.2 m

Explanation

For constant velocity, distance equals speed multiplied by time: 6.0 m/s × 25 s = 150 m. No acceleration term is needed because the velocity does not change.

Question 28Physics: mechanics, forces, energy, electricity and magnetism, waves

A skydiver falls at terminal velocity. Which statement correctly describes the forces acting on the skydiver at that instant?

  1. The downward weight is larger than the drag force, so the skydiver still accelerates.
  2. The drag force is larger than the weight, so the skydiver decelerates.
  3. No forces act on the skydiver because the speed is constant.
  4. The upward drag force equals the downward weight, so the net force is zero. Correct answer.

Explanation

Terminal velocity means the speed is constant, so by Newton's first law the net force must be zero. The two vertical forces, weight downwards and air resistance upwards, must therefore be equal in magnitude.

Question 29Physics: mechanics, forces, energy, electricity and magnetism, waves

A force of 40 N is applied to a lever arm at a perpendicular distance of 0.50 m from the pivot. What is the moment of this force about the pivot?

  1. 20 N·m Correct answer.
  2. 80 N·m
  3. 40 N·m
  4. 0.0125 N·m

Explanation

The moment of a force is the product of the force and the perpendicular distance from the pivot: 40 N × 0.50 m = 20 N·m. The distance must be measured perpendicular to the line of action of the force.

Question 30Physics: mechanics, forces, energy, electricity and magnetism, waves

A spring obeys Hooke's law with a spring constant of 200 N/m. What force is needed to stretch it by 0.15 m within the elastic limit?

  1. 30 N Correct answer.
  2. 0.00075 N
  3. 1333 N
  4. 215 N

Explanation

Hooke's law states F = kx, so the force is 200 N/m × 0.15 m = 30 N. The extension must remain within the elastic limit for the law to apply.

Question 31Physics: mechanics, forces, energy, electricity and magnetism, waves

A machine does 600 J of useful work while taking in 1000 J of energy. What is the efficiency of the machine?

  1. 0.6 J
  2. 60% Correct answer.
  3. 167%
  4. 40%

Explanation

Efficiency is useful output energy divided by total input energy, expressed as a percentage: (600/1000) × 100% = 60%. The remaining 400 J is wasted, usually as heat.

Question 32Physics: mechanics, forces, energy, electricity and magnetism, waves

A current of 0.50 A flows through a lamp for 2.0 minutes. How much charge passes through the lamp?

  1. 60 C Correct answer.
  2. 1.0 C
  3. 0.0042 C
  4. 240 C

Explanation

Charge equals current multiplied by time in seconds: Q = It = 0.50 A × 120 s = 60 C. The time must be converted from minutes to seconds before multiplying.

Question 33Physics: mechanics, forces, energy, electricity and magnetism, waves

A 2.0 kg object is lifted vertically through 3.0 m at constant speed. Taking g = 10 m/s², how much gravitational potential energy does it gain?

  1. 60 J Correct answer.
  2. 20 J
  3. 6.7 J
  4. 0 J

Explanation

The gain in gravitational potential energy is mgh = 2.0 kg × 10 m/s² × 3.0 m = 60 J. Constant speed means no kinetic energy change, so all the work goes into potential energy.

Question 34Physics: mechanics, forces, energy, electricity and magnetism, waves

A 1500 kg car travelling at 20 m/s brakes to rest. What is the kinetic energy lost by the car?

  1. 15 kJ
  2. 600 kJ
  3. 30 kJ
  4. 300 kJ Correct answer.

Explanation

Kinetic energy is ½mv² = ½ × 1500 kg × (20 m/s)² = 300 000 J = 300 kJ. This energy is converted mainly into thermal energy in the brakes.

Question 35Physics: mechanics, forces, energy, electricity and magnetism, waves

A ball is thrown vertically upwards with an initial speed of 20 m/s. Taking g = 10 m/s² and ignoring air resistance, how long does it take to reach its highest point?

  1. 20 s
  2. 4.0 s
  3. 0.50 s
  4. 2.0 s Correct answer.

Explanation

At the highest point the vertical velocity is zero, so using v = u − gt gives 0 = 20 − 10t, hence t = 2.0 s. The acceleration due to gravity acts opposite to the upward motion.

Question 36Physics: mechanics, forces, energy, electricity and magnetism, waves

A block of mass 4.0 kg is pulled along a rough horizontal floor by a horizontal force of 30 N. A constant friction force of 10 N opposes the motion. What is the acceleration of the block?

  1. 10 m/s²
  2. 2.5 m/s²
  3. 7.5 m/s²
  4. 5.0 m/s² Correct answer.

Explanation

The net horizontal force is 30 N − 10 N = 20 N. Using Newton's second law, a = F/m = 20 N / 4.0 kg = 5.0 m/s².

Question 37Physics: mechanics, forces, energy, electricity and magnetism, waves

Two point charges repel each other with a force F when separated by a distance d. If the separation is doubled while the charges stay the same, what is the new force?

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

Explanation

Coulomb's law states the force is inversely proportional to the square of the separation. Doubling d multiplies the denominator by 4, so the force becomes F/4.

Question 38Physics: mechanics, forces, energy, electricity and magnetism, waves

A charge of 5.0 C is moved through a potential difference of 12 V. How much energy is transferred?

  1. 2.4 J
  2. 0.42 J
  3. 17 J
  4. 60 J Correct answer.

Explanation

The energy transferred is the product of charge and potential difference: W = QV = 5.0 C × 12 V = 60 J. One volt is one joule per coulomb.

Question 39Physics: mechanics, forces, energy, electricity and magnetism, waves

A sinusoidal wave has a period of 0.020 s. What is its frequency?

  1. 50 Hz Correct answer.
  2. 0.50 Hz
  3. 0.020 Hz
  4. 20 Hz

Explanation

Frequency is the reciprocal of the period: f = 1/T = 1/0.020 s = 50 Hz. The period is the time for one complete oscillation.

Question 40Physics: mechanics, forces, energy, electricity and magnetism, waves

A convex lens forms a real image of a distant object at 20 cm from the lens. What is the focal length of the lens?

  1. 40 cm
  2. 20 cm Correct answer.
  3. 0.05 cm
  4. 10 cm

Explanation

Rays from a very distant object arrive nearly parallel and converge at the principal focus. The image distance therefore equals the focal length, 20 cm.

Question 41Physics: mechanics, forces, energy, electricity and magnetism, waves

A 12 V supply is connected to two resistors of 3.0 Ω and 6.0 Ω in series. What current flows in the circuit?

  1. 2.0 A
  2. 1.3 A Correct answer.
  3. 4.0 A
  4. 6.0 A

Explanation

In series the resistances add: R = 3.0 + 6.0 = 9.0 Ω. Then I = V/R = 12 V / 9.0 Ω ≈ 1.3 A.

Question 42Physics: mechanics, forces, energy, electricity and magnetism, waves

A straight wire carrying a current is placed at right angles to a uniform magnetic field. Which change alone would double the magnitude of the magnetic force on the wire?

  1. Reversing the direction of the current
  2. Reducing the magnetic flux density to half its value
  3. Doubling the current while keeping the same length in the field Correct answer.
  4. Rotating the wire so it lies parallel to the field

Explanation

The force on a current-carrying wire is F = BIL sin θ, so force is directly proportional to current. Doubling the current doubles the force while keeping the field, length and angle unchanged.

Question 43Physics: mechanics, forces, energy, electricity and magnetism, waves

Electromagnetic induction occurs when a magnet is pushed into a coil. Which change would increase the induced electromotive force?

  1. Pushing the magnet into the coil more quickly Correct answer.
  2. Keeping the magnet stationary inside the coil
  3. Replacing the coil with a straight piece of wire
  4. Using a coil with fewer turns

Explanation

Faraday's law states that the induced emf is proportional to the rate of change of magnetic flux linkage. Moving the magnet faster increases that rate and so increases the emf.

Question 44Physics: mechanics, forces, energy, electricity and magnetism, waves

A spring of spring constant 400 N/m is compressed by 0.10 m and used to launch a 0.20 kg ball horizontally on a frictionless surface. What is the speed of the ball as it leaves the spring?

  1. 0.45 m/s
  2. 2.0 m/s
  3. 20 m/s
  4. 4.5 m/s Correct answer.

Explanation

Elastic potential energy stored is ½kx² = ½ × 400 × 0.10² = 2.0 J. All of this becomes kinetic energy, so v = √(2E/m) = √(4.0/0.20) ≈ 4.5 m/s.

Question 45Physics: mechanics, forces, energy, electricity and magnetism, waves

A 6.0 V battery of negligible internal resistance is connected to a 4.0 Ω resistor in parallel with an 8.0 Ω resistor. What is the total current drawn from the battery?

  1. 1.5 A
  2. 2.25 A Correct answer.
  3. 0.75 A
  4. 0.25 A

Explanation

The parallel combination is (4.0 × 8.0)/(4.0 + 8.0) = 32/12 ≈ 2.67 Ω. The total current is then I = V/R = 6.0/2.67 ≈ 2.25 A, which also equals 1.5 A + 0.75 A in the two branches.

Question 46Physics: mechanics, forces, energy, electricity and magnetism, waves

A wave pulse travels along a stretched string. The tension in the string is increased to four times its original value while the string and its mass per unit length stay the same. How does the wave speed change?

  1. It becomes four times larger.
  2. It stays the same.
  3. It halves.
  4. It doubles. Correct answer.

Explanation

The speed of a transverse wave on a string is v = √(T/μ), so speed is proportional to the square root of tension. Quadrupling the tension doubles the speed.

Question 47Physics: mechanics, forces, energy, electricity and magnetism, waves

A ball is dropped from rest from a height h above the ground. Ignoring air resistance, which statement about its motion just before impact is correct?

  1. Its kinetic energy is twice the gravitational potential energy lost, and its speed is 2√(gh).
  2. Its kinetic energy is half the gravitational potential energy lost, and its speed is √(gh).
  3. Its kinetic energy is zero because the potential energy has not changed.
  4. Its kinetic energy equals the gravitational potential energy lost, and its speed is √(2gh). Correct answer.

Explanation

Energy is conserved, so the potential energy lost mgh becomes kinetic energy ½mv². Equating them gives v² = 2gh, so the speed just before impact is √(2gh).

Question 48Physics: mechanics, forces, energy, electricity and magnetism, waves

A sound source moves towards a stationary observer. Compared with the frequency emitted by the source, what does the observer detect?

  1. A lower frequency, because the wavefronts are stretched apart
  2. A higher frequency, because successive wavefronts arrive closer together Correct answer.
  3. A higher frequency, because the speed of sound increases towards the observer
  4. The same frequency, because the speed of sound is unchanged

Explanation

When the source approaches, each wavefront is emitted from a position closer to the observer, so the wavelength is shortened. Since the speed of sound in air is essentially fixed, a shorter wavelength means a higher observed frequency.

Question 49Physics: mechanics, forces, energy, electricity and magnetism, waves

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

  1. 3.0 m/s in the original direction of motion
  2. 0.50 m/s opposite to the original direction
  3. 1.5 m/s in the original direction of motion
  4. 1.0 m/s in the original direction of motion Correct answer.

Explanation

Momentum is conserved in the collision: (2.0 × 3.0) + 0 = (2.0 + 4.0) × v, giving 6.0 = 6.0v, so v = 1.0 m/s. The combined mass moves in the original direction of the moving trolley.

Question 50Physics: mechanics, forces, energy, electricity and magnetism, waves

A student builds a circuit with a 9.0 V battery of negligible internal resistance connected to two resistors of 6.0 Ω and 3.0 Ω wired in parallel with each other. What is the total current drawn from the battery?

  1. 13.5 A
  2. 1.0 A
  3. 1.5 A
  4. 4.5 A Correct answer.

Explanation

For resistors in parallel the reciprocals of the resistances add: 1/R = 1/6.0 + 1/3.0 = 1/6.0 + 2/6.0 = 3/6.0, so the equivalent resistance is 2.0 Ω. The current from the battery is then I = V/R = 9.0 V ÷ 2.0 Ω = 4.5 A. The parallel combination always has a resistance smaller than the smallest branch resistor, which is why the current exceeds that through either branch alone.