Physical Science: Matter, Forces & Energy — Grade 8 Science — Cumulative Final worked answers

Student exam paper

Original cumulative physical-science paper with evidence, model, graph and calculation reasoning. All records are supplied illustrative cases. It is not an official New York State test.

40 questions · 120 points · suggested 135 minutes

Student instructions

  1. Work independently before opening the separate answer key.
  2. Use only the supplied reference relationships and a basic calculator; show methods and units.
  3. Explain observations, mechanisms and model assumptions in sentences or labeled drawings.
  4. Each question has three criterion marks; equivalent supported explanations are accepted.
  5. Written responses remain awaiting human review until the parent or teacher assigns valid marks.

Permitted reference relationships

QuantityRelationship / condition
Densitymass / volume
Average speed; velocitydistance / time; displacement / time
Accelerationnet force / mass
Weightmass × supplied gravitational field
Pressure; forceforce / area; pressure × area
Aligned-force workconstant force × displacement
Kinetic energy½ × mass × speed²
Powerenergy transferred / elapsed time
Efficiencyuseful output / input × 100%
Wave relationspeed = frequency × wavelength
Frequencycomplete cycles / time
Simple resistor currentvoltage / resistance
Mean; rangesum / count; maximum − minimum

Coverage and marks

ChapterQuestionsPoints
Properties of Matter1, 2, 3, 4, 515
Phases of Matter6, 7, 8, 9, 1015
Chemistry11, 12, 13, 14, 1515
Forces16, 17, 18, 19, 2015
Motion21, 22, 23, 24, 2515
Work & Machines26, 27, 28, 29, 3015
Energy & Heat Transfer31, 32, 33, 34, 3515
Waves, Sound & Light36, 37, 38, 39, 4015

Parent / teacher marking guide

Question 1 · 3 points

A record has 9 protons, 10 neutrons and 10 electrons. Find atomic number, mass number and charge. Would removing one electron change its element?

Worked answer

Atomic number 9; mass number 19; charge −1. Removing one electron gives a neutral particle of the same element because proton count remains 9.

Use proton count to identify the atomic number.

Add 9+10 for mass number and compare 9 positive with 10 negative charges.

Element identity changes only with proton count, not an electron change.

Marking criteria

Question 2 · 3 points

A supplied sample melts and later reacts to form a new substance. Explain the distinction and evaluate the claim that every hard-to-reverse change is chemical.

Worked answer

Melting is physical if identity is retained; a reaction forms a different substance. Reversibility alone is not the defining criterion, so a hard-to-reverse physical change can still be physical.

Classify by substance identity.

Distinguish a visible change from evidence of a new substance.

Test the reversibility rule against the identity definition.

Marking criteria

Question 3 · 3 points

A model block is 90 g and 30 cm³; another hollow object is 90 g and encloses 150 cm³. Use water density 1 g/cm³ to compare floating tendencies and name a hollow-object assumption.

Worked answer

Densities are 3 and 0.6 g/cm³. The solid block tends to sink; the hollow object can float if it retains its enclosed volume and can displace sufficient water. Equal mass does not mean equal density.

Divide each mass by the stated effective volume.

Compare with modeled water density.

Account for shape, leaks or other support effects before generalizing.

Marking criteria

Question 4 · 3 points

Main-group records have proton counts 12 and 13, with two and three outer electrons respectively. Explain their atomic-number order, one use of outer-electron patterns and a limit of the shell model.

Worked answer

Atomic number orders 12 before 13. Outer electrons help explain characteristic bonding patterns for these main-group cases, but the shell picture is a simplified energy representation rather than literal planetary electron tracks.

Use protons for atomic-number order.

Connect outer electrons with bonding patterns.

Qualify a shell drawing and simplified group rules.

Marking criteria

Question 5 · 3 points

Illustrative leak tests give A 0/4 leaks and B 1/4, while reuse tests give A 3 cycles and B 25. Choose provisionally for a leak-sensitive task and specify evidence needed for a broader environmental comparison.

Worked answer

A has the stronger supplied leak record for that task. B’s longer tested reuse lifetime matters to repeated use. Resource extraction, production energy, actual reuse and disposal evidence are needed before making a whole-impact claim.

State the intended design criterion.

Compare both performance records rather than one label.

Identify specific unmeasured life-cycle evidence.

Marking criteria

Question 6 · 3 points

A sealed pure-water sample changes from 40 g ice to 15 g ice plus 25 g liquid. Explain the mass and particle identities, and correct a drawing that makes water molecules larger as it melts.

Worked answer

The total remains 40 g and the particles retain water identity. Arrangement and motion change during melting; individual molecules do not grow simply because state changes.

Add the two phase masses.

Separate state from substance identity.

Revise spacing and motion rather than molecular size.

Marking criteria

Question 7 · 3 points

Samples of the same substance and phase have masses 50 and 200 g at 30 °C. Explain why temperature alone does not compare total internal energy and state the net transfer direction when a 45 °C sample contacts a 30 °C one.

Worked answer

Equal temperature relates to comparable average particle-motion conditions, while amount and interactions also affect internal energy. The larger sample can contain more internal energy. Net thermal transfer is from warmer toward cooler under the stated contact conditions.

Separate average-related temperature from total amount.

Keep substance and phase comparable.

State the thermal transfer direction without treating cold as a material.

Marking criteria

Question 8 · 3 points

A fixed gas sample at matched temperature has modeled absolute pressures 90 kPa at 50 mL and 150 kPa at 30 mL. Check the products and explain why this does not mean particles shrink.

Worked answer

Both products are 4,500 kPa·mL. The smaller volume gives greater pressure under the fixed-temperature, fixed-amount model. The particles retain their sizes, while reduced space changes wall-impact frequency.

Calculate 90×50 and 150×30.

Identify the fixed amount and temperature assumptions.

Use spacing and collisions rather than particle shrinkage.

Marking criteria

Question 9 · 3 points

A cold intact cup containing red water develops clear outside droplets. A wet towel dries at 24 °C. Explain water sources and destinations in both cases without creation or destruction.

Worked answer

Outside water can condense from vapor in the surrounding air rather than leak as red contents. Towel water can evaporate at the surface below boiling and enter the air as normally invisible vapor. The visible droplets and gaseous vapor are different states of existing water.

Use the boundary and clear/red comparison.

Explain evaporation below boiling.

Account for existing water and distinguish gas from visible droplets.

Marking criteria

Question 10 · 3 points

A pure-water model stays near 0 °C while ice melts. A heater supplies 80 J/min for 5 min. Calculate input and explain the plateau, including a real-apparatus limitation.

Worked answer

Input is 400 J. In the ideal model, energy changes phase fraction and particle interactions while temperature remains near steady. Real container warming and transfers to surroundings can account for part of the input.

Multiply rate by duration.

Explain continued input during phase change.

State boundary, pressure, purity or heat-loss assumptions.

Marking criteria

Question 11 · 3 points

Supplied case A bubbles while pure water boils; case B bubbles while composition tests establish a different gas product. Decide which is chemical and explain why the same visible sign cannot decide both cases alone.

Worked answer

A is a physical phase change retaining water identity; B is chemical under the supplied new-product evidence. Bubbles are an observation consistent with different causes, so composition and characteristic-property evidence matter.

Separate the observation from interpretation.

Use identity evidence in each supplied case.

Reject a sign-alone universal rule.

Marking criteria

Question 12 · 3 points

A reaction’s open apparatus drops from 68.0 to 66.2 g while a gas escapes. A complete sealed-apparatus comparison retains its starting reading. Explain the 1.8 g difference with a system boundary and atom model.

Worked answer

The open measured system can lose 1.8 g gas across its boundary. Including that escaped matter reconciles the account; rearranged atoms form products without being destroyed. The sealed apparatus retains matter, though it can still exchange energy.

Calculate the 1.8 g measured difference.

Identify the different matter boundary conditions.

Connect atom rearrangement with conserved mass.

Marking criteria

Question 13 · 3 points

Balance N₂ + H₂ → NH₃. Count both atom types and explain why changing NH₃ to NH₂ is not a balancing method.

Worked answer

N₂ + 3H₂ → 2NH₃ has two N and six H atoms on each side. Coefficients change whole-particle counts; changing NH₃ to NH₂ changes the represented composition and intended substance.

Balance nitrogen with two NH₃ units.

Supply six hydrogen atoms with three H₂ units.

Keep formulas fixed while changing coefficients.

Marking criteria

Question 14 · 3 points

A simplified reaction requires 70 energy units for bond breaking and releases 110 when new bonds form. Find the net transfer and classify the process. Explain the role of bond breaking.

Worked answer

Net 40 units transfer outward, so the overall process is exothermic. Bond breaking requires energy; release on bond formation is larger in this model. An overall warm-up does not imply breaking bonds releases energy.

Compare required and released quantities.

Calculate 110−70=40 outward units.

Separate the contributions from the net reaction classification.

Marking criteria

Question 15 · 3 points

Supplied dilute aqueous samples near room temperature have pH 4, 7 and 10. Classify them, propose a safe indication method and explain why a neutral sample is not automatically drinkable.

Worked answer

They are acidic, approximately neutral and basic under the stated conditions. Use supplied records or a suitable approved indicator, never taste unknowns. Neutral pH does not exclude harmful substances or microorganisms and does not identify complete composition.

Apply the stated pH reference conditions.

Choose evidence without tasting or touch-testing unknowns.

Separate acid–base character from drinking safety.

Marking criteria

Question 16 · 3 points

A cart already moving left has 11 N right and 5 N left horizontal forces. Find net force and explain whether it must instantly move right.

Worked answer

Net force is 6 N right. It accelerates right under the simple model and may initially slow its leftward motion; instantaneous velocity requires its prior state and time. Force direction does not set velocity immediately.

Combine directional forces on the cart.

Separate acceleration from velocity.

State the missing motion history or time information.

Marking criteria

Question 17 · 3 points

A hand pushes a cart rightward with 9 N and floor resistance acts leftward with 4 N. Give the cart’s net force and the cart-on-hand force. Explain why they are different quantities.

Worked answer

The cart’s horizontal net force is 5 N right. The cart pushes the hand with 9 N left as the interaction partner. That partner acts on the hand and cannot be added in the cart’s diagram.

Calculate 9−4 for forces on one receiver.

Identify the 9 N opposite interaction force on the hand.

Distinguish an interaction pair from a net-force sum.

Marking criteria

Question 18 · 3 points

Use g=10 N/kg near modeled Earth and g=2 N/kg at another modeled location for the same 3 kg object. Calculate both weights and explain which quantity stays fixed.

Worked answer

Weights are 30 N and 6 N. The object’s mass stays 3 kg; changing gravitational field changes its weight. The supplied fields are model values, not complete location-independent laws.

Use weight=mass×field strength.

Compute both force values with N units.

Distinguish mass from gravitational force.

Marking criteria

Question 19 · 3 points

Repeated movement records for a fixed magnet and clip are 3/3 at 1 cm, 2/3 at 2 cm and 0/3 at 5 cm on the same surface. Explain the supported pattern and why this is not a direct force measurement.

Worked answer

Movement becomes less frequent at greater separation in this supplied setup, consistent with a weaker interaction relative to the motion threshold. Friction and resetting affect movement. The counts do not directly measure force or establish a universal distance formula.

Use all three repeated records.

Connect the gap interaction with a field model.

Separate movement threshold from measured force and identify controls.

Marking criteria

Question 20 · 3 points

An ideal connected fluid has pressure 3,000 Pa at pistons of areas 0.02 and 0.06 m². Find forces and explain the displacement trade-off needed for a no-loss lift.

Worked answer

Forces are 60 and 180 N. Equal displaced volumes give the large piston one-third the small piston’s displacement, so its larger force does not produce free work. Real systems can have losses.

Use F=pressure×area.

Compute 60 and 180 N.

Connect volume balance, displacement and energy accounting.

Marking criteria

Question 21 · 3 points

A walker travels 45 m north and 15 m south in 30 s. Choose north positive and find distance, displacement, average speed and average velocity.

Worked answer

Distance is 60 m and displacement +30 m. Average speed is 2 m/s and average velocity +1 m/s north. The averages do not establish the instantaneous speeds during the trip.

Add path lengths for distance.

Subtract opposite-direction travel for displacement.

Divide each quantity by the common elapsed time with appropriate direction.

Marking criteria

Question 22 · 3 points

Positions at 0, 3, 6 and 9 s are 0, 9, 9 and 3 m. Calculate interval velocities and explain what the horizontal segment means on these axes.

Worked answer

Interval velocities are +3, 0 and −2 m/s. The 3–6 s horizontal position segment means unchanged position, while the last interval moves in the negative direction in the straight-segment model. A horizontal velocity graph would have a different meaning.

Use position change divided by interval time.

Compute the three signed slopes.

Read the actual axes before interpreting horizontal or falling lines.

Marking criteria

Question 23 · 3 points

A 5 kg cart experiences a 15 N net force. Find acceleration; predict it for a 10 kg cart under the same net force. Does the reaction partner act on the same cart?

Worked answer

Accelerations are 3 and 1.5 m/s². Doubling mass halves acceleration at fixed net force. A particular interaction’s partner acts on the other object, not on the same cart.

Use a=Fnet/m for both masses.

Keep net force fixed in the comparison.

Name separate receivers for an interaction pair.

Marking criteria

Question 24 · 3 points

Matched collision records give bumper thickness 18 mm before, 10 mm during and 18 mm after. Peak forces are 14 N with padding and 28 N without. Explain deformation and the bounded force comparison.

Worked answer

The bumper has temporary elastic deformation in this model. The padded peak is half the unpadded peak under the matched conditions. This supports that comparison, not certification of all protectors or a complete force–time account.

Use before–during–after evidence.

Calculate the peak ratio.

State a geometry, material, trial or safety-generalization limit.

Marking criteria

Question 25 · 3 points

A protector allows at most 4 cm thickness. A has mean peak 16 N and thickness 3 cm; B has mean peak 11 N and thickness 6 cm. Choose a qualifying starting design and propose a measured revision.

Worked answer

A qualifies; B violates the thickness constraint. Investigate a new arrangement within 4 cm, retesting at matched starting motion and measuring repeated peaks and permanent deformation. A proposal is not improved performance until tested.

Separate the hard limit from the peak-force criterion.

Select A under the supplied constraint.

Specify a controlled retest and relevant outcomes for a revision.

Marking criteria

Question 26 · 3 points

A constant 7 N force acts along a 2 m displacement. Find work and compare with holding the same object motionless. Explain why bodily effort need not match work on the object.

Worked answer

Aligned-force work is 14 J. The held object has zero displacement and zero ideal mechanical work by the holding force, while a person can still expend metabolic energy.

Use constant aligned-force work Fd.

Calculate 14 J and the zero-displacement comparison.

Distinguish the chosen object’s mechanical account from the person’s physiology.

Marking criteria

Question 27 · 3 points

Ideal ramps lift the same 8 N load by 0.3 m over paths 0.6 and 1.2 m. Find ideal input forces and explain what actual friction changes.

Worked answer

Output work is 2.4 J in both. Ideal input forces are 4 and 2 N, so a longer distance trades for lower force. Friction increases input work and transfers energy into other pathways.

Find output work 8×0.3.

Divide work by each along-ramp path.

Qualify the no-loss assumption and account for actual friction.

Marking criteria

Question 28 · 3 points

An ideal machine uses 12 N over 0.9 m to apply 36 N over 0.3 m. Find mechanical advantage and both works; evaluate a claim of 300% energy efficiency.

Worked answer

Mechanical advantage is 3. Input and output works are both 10.8 J, so ideal energy efficiency is 100%, not 300%. The force gain is paired with a distance reduction.

Calculate output/input force ratio.

Calculate both force–distance products.

Distinguish force ratio from energy ratio.

Marking criteria

Question 29 · 3 points

A machine receives 360 J and delivers 270 J useful lifting work. Find efficiency and the other energy amount. Would calling it waste make that energy disappear?

Worked answer

Efficiency is 75%; 90 J is in other pathways or stored changes under the chosen account. It does not disappear, and usefulness depends on the task.

Calculate 270/360×100%.

Subtract to account for 90 J.

Distinguish conservation from the defined useful output.

Marking criteria

Question 30 · 3 points

Devices A and B each deliver 300 J, taking 10 and 15 s. Their inputs are 500 and 375 J. Compare useful power and efficiency.

Worked answer

A supplies 30 W at 60% efficiency; B supplies 20 W at 80%. A is faster, while B has the larger useful input fraction. The comparisons answer different questions.

Divide delivered energy by time.

Divide useful output by input.

Keep units and the purpose of each ratio distinct.

Marking criteria

Question 31 · 3 points

For a fixed 4 kg cart, calculate kinetic energy at 1 and 3 m/s. Compare with an 8 kg cart at 1 m/s and explain the separate speed and mass relationships.

Worked answer

The 4 kg cart has 2 and 18 J; tripling speed multiplies energy by nine. The 8 kg cart at 1 m/s has 4 J, double the fixed-speed 4 kg case. Mass and speed must be varied separately to isolate their effects.

Apply KE=½mv² with the stated units.

Compare the squared-speed ratio.

Compare doubled mass at fixed speed.

Marking criteria

Question 32 · 3 points

A model lamp receives 500 J electrical energy, with 125 J visible light and 375 J other mainly thermal output. Give the useful light fraction and a complete transfer account.

Worked answer

The useful light fraction is 25%; 125+375=500 J accounts for the input. Different output forms and transfers do not imply destruction; usefulness is defined for lighting.

Find the light/input ratio.

Add all supplied outputs.

Explain transfer across the device boundary and purpose-dependent usefulness.

Marking criteria

Question 33 · 3 points

Equal cool-water cups warm by 7 °C unwrapped and 3 °C with both insulation and a lid. Explain the transfer direction and design follow-up tests separating the two changes.

Worked answer

Net energy enters from warmer surroundings. Compare wall-only, lid-only and unmodified matched cups with equal volume, start temperature and observation conditions. Contact, moving-fluid, radiation and evaporation pathways can differ; changing two features does not isolate one.

Describe cooler water gaining energy from warmer surroundings.

Identify insulation and lid as two changed features.

Specify matched follow-ups with a relevant mechanism and limitation.

Marking criteria

Question 34 · 3 points

A rolling model begins with 120 J mechanical energy. Later it has 75 J mechanical, 35 J additional thermal energy inside the boundary and 10 J transferred outside. Reconcile the account and distinguish closed from isolated.

Worked answer

75+35+10=120 J. Mechanical energy falls by 45 J while the complete account conserves energy. A boundary closed to matter can exchange energy; an isolated ideal system exchanges neither.

Sum stored changes and outward transfer.

Calculate the mechanical decrease.

Identify the relevant boundary distinction.

Marking criteria

Question 35 · 3 points

An ideal 9 V source drives a 6 Ω resistor in a complete loop. Find current, predict it when the path is broken and explain why a resistor does not consume charge.

Worked answer

Current is 1.5 A in the simple resistive model; a broken path prevents the sustained loop current. Charge circulates while energy transfers to the resistor and surroundings. The source and resistor model has stated ideal assumptions.

Apply I=V/R for the complete loop.

Identify the missing return path after a break.

Separate charge flow from energy transfer.

Marking criteria

Question 36 · 3 points

Sources A/B/C have amplitudes 2/5/2 mm and complete 3/3/5 cycles in 0.01 s. Compare frequency, pitch and amplitude without claiming exact perceived loudness.

Worked answer

A and B are 300 Hz; C is 500 Hz and generally has higher pitch. B has the largest amplitude. Received loudness also depends on distance, medium and receiver response.

Divide complete cycle counts by the interval.

Distinguish amplitude from frequency and pitch.

Qualify a received-loudness prediction.

Marking criteria

Question 37 · 3 points

Two modeled waves have speed 20 m/s and frequencies 4 and 10 Hz. Find wavelengths and explain why a spatial snapshot alone does not determine hertz.

Worked answer

Wavelengths are 5 and 2 m using v=fλ. Frequency requires cycles per time; a displacement–position snapshot directly represents spatial repetition, not the time rate without additional information.

Divide common speed by each frequency.

Give metre units.

Distinguish spatial and time axes.

Marking criteria

Question 38 · 3 points

An echo returns in 0.40 s with modeled sound speed 330 m/s. Find one-way distance and explain why the airborne path needs matter without moving one parcel of air the entire distance.

Worked answer

Round-trip distance is 132 m, so one-way distance is 66 m. Successive particle interactions transmit the disturbance while particles mainly oscillate locally. Ordinary airborne sound needs a material medium.

Multiply speed by round-trip time.

Halve for one-way distance.

Explain the material mechanism and local particle motion.

Marking criteria

Question 39 · 3 points

A supplied light account gives 200 units incident, 50 reflected and 120 transmitted. Find the absorbed amount and explain a mechanism distinction between light and ordinary sound across a vacuum.

Worked answer

Absorbed amount is 30 units. Light can cross a vacuum as an electromagnetic disturbance; ordinary sound requires material interactions. A ray account tracks paths and energy but omits some wave detail.

Subtract reflected and transmitted portions from the input.

Check 50+120+30=200.

Distinguish transmission mechanisms and a model limitation.

Marking criteria

Question 40 · 3 points

A receiver uses threshold 0.5: below is 0 and at least is 1. Values are 0.2, 0.6, 0.51 and 0.1. Decode them, identify the most threshold-sensitive value and trace a moving-coil speaker to an air receiver.

Worked answer

The sequence is 0110, with 0.51 nearest the threshold and most sensitive to a small noise change. A changing current produces a coil–magnet interaction, membrane motion, successive air interactions and receiver response. Digital symbols do not prevent all error.

Apply the supplied threshold rule.

Compare distance from the decision boundary.

Include the intermediate speaker and medium mechanisms.

Marking criteria

Revisit the covered chapters

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