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

Parent / teacher answer key

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

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

Permitted reference relationships

Quantity	Relationship / condition
Density	mass / volume
Average speed; velocity	distance / time; displacement / time
Acceleration	net force / mass
Weight	mass × supplied gravitational field
Pressure; force	force / area; pressure × area
Aligned-force work	constant force × displacement
Kinetic energy	½ × mass × speed²
Power	energy transferred / elapsed time
Efficiency	useful output / input × 100%
Wave relation	speed = frequency × wavelength
Frequency	complete cycles / time
Simple resistor current	voltage / resistance
Mean; range	sum / count; maximum − minimum

Coverage and marks

Chapter	Questions	Points
Properties of Matter	1, 2, 3, 4, 5	15
Phases of Matter	6, 7, 8, 9, 10	15
Chemistry	11, 12, 13, 14, 15	15
Forces	16, 17, 18, 19, 20	15
Motion	21, 22, 23, 24, 25	15
Work & Machines	26, 27, 28, 29, 30	15
Energy & Heat Transfer	31, 32, 33, 34, 35	15
Waves, Sound & Light	36, 37, 38, 39, 40	15

Name: ____________________ Date: ____________________

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?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Question 13 · 3 points

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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?

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.

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.

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.

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.

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.

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?

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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