Physical Science: Matter, Forces & Energy — Grade 8 Science — Midterm
Parent / teacher answer keyOriginal 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.
20 questions · 60 points · suggested 90 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 |
Name: ____________________ Date: ____________________
Question 1 · 3 points
Two neutral atoms each have 6 protons but have 6 and 8 neutrons. Give their mass numbers and electron counts; explain why they are isotopes.
Question 2 · 3 points
Cutting a metal sheet changes its shape; a supplied reaction changes that metal into a different compound. Compare classification and evidence, without using “looks different” as your only reason.
Question 3 · 3 points
A sample of mass 54 g occupies 20 cm³. A matched material sample has twice both values. Find both densities and explain why the larger sample need not sink more merely because it is heavier.
Question 4 · 3 points
An element has 10 protons and another 11. State atomic-number order and explain whether electron gain would move either to the next element. Include a limit of a simplified electron-shell picture.
Question 5 · 3 points
Material P survives 5 model uses and Q 30, but Q has an unknown leak rate. Explain why longer life alone does not settle a wet-use container choice and name two missing measurements.
Question 6 · 3 points
A 60 g sealed pure-water sample freezes from liquid to ice. Explain mass, identity and particle arrangement, and predict the effect of later melting on the classification.
Question 7 · 3 points
Two same-phase water samples at 20 °C have different masses. A student says they must contain identical total internal energy. Correct the claim and explain the distinction between heat and temperature.
Question 8 · 3 points
A fixed gas at matched temperature is modeled at 110 kPa in 40 mL and 220 kPa in 20 mL. Check the relation and explain what changes between particles.
Question 9 · 3 points
Supplied air has dew point 10 °C. Cup surfaces are 6 and 16 °C. Predict the condensation comparison and explain why a puddle can evaporate in the same room without boiling.
Question 10 · 3 points
A modeled heater supplies 60 J/min while a pure-water melting plateau lasts 6 min. Find the input, explain the flat temperature and name a condition that would change the real graph.
Question 11 · 3 points
A student observes cloudiness after mixing and calls it proof of a reaction. Explain a supported next step and why a visible clue alone is not enough.
Question 12 · 3 points
An open apparatus falls from 83.0 to 80.5 g while a gas leaves. Account for the change and explain what a sealed comparison would need to weigh.
Question 13 · 3 points
Balance C + O₂ → CO₂ and compare it with a proposed product CO. Explain why balancing cannot silently replace one product formula with another.
Question 14 · 3 points
A simplified reaction requires 95 units for breaking bonds and releases 65 from forming bonds. Explain the net energy direction, classification and why bond breaking is not the release step.
Question 15 · 3 points
Near-room-temperature dilute aqueous samples have pH 2 and 9. Classify them and explain why neither taste nor pH alone is an appropriate way to identify an unknown household chemical.
Question 16 · 3 points
A cart has horizontal forces 12 N left and 12 N right and is already moving steadily. Explain net force and whether “it must stop” follows.
Question 17 · 3 points
A book rests on a table. Its weight and support force are equal. Explain why these are not a third-law pair and name the receivers of their actual partners.
Question 18 · 3 points
A 4 kg model object is in a 9 N/kg gravitational field. Calculate weight and explain how a friction comparison could isolate surface type.
Question 19 · 3 points
A clip moves near a magnet across a paper gap. The same clip does not move farther away. Explain what this supports and which other factor could affect the motion threshold.
Question 20 · 3 points
An ideal fluid transmits 1,500 Pa to areas 0.02 and 0.08 m². Find forces and explain why the larger force does not generate free work.