Practice Test 2 - Middle School Physical Science

20 questions. Answer them in any order, then submit to see your score and every explanation.

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1. A student adds baking soda (white powder) to vinegar (clear liquid) in a flask and quickly places a balloon over the opening. After 30 seconds: the balloon inflates, the liquid continues fizzing, and the flask feels cooler than before. Which observation most clearly indicates that a chemical reaction occurred (not just a physical change like dissolving)?
2. A student tries to "count how many molecules" are in a grain of table salt ($\mathrm{NaCl}$). Why is this not the right way to describe the structure of salt?
3. A student investigates a magnetic field by placing a small compass at 5 different positions around a bar magnet (same distance from the magnet each time). At each position, the student records the direction the compass needle points and draws arrows on a paper map. Does this investigation provide good evidence that a magnetic field exists around the magnet, and what would most improve it?
4. Complete the conservation check for the particle model $2\text{Na} + \text{Cl}_2 \rightarrow 2\text{NaCl}$. Which counts are correct?
5. Two students send a simple message using a flashlight: short flashes mean "dot" and long flashes mean "dash" (like Morse code). Which wave property is being changed to encode the message?
6. A student tests the same cart with several net forces and records acceleration. Which calculation would stay constant for every trial if the cart's mass does not change?
7. A student adds a scoop of powdered drink mix to a cup of water. Before: - Water: clear liquid, 20°C, no smell - Drink mix: orange powder, sweet smell, dry After stirring: - Mixture: orange liquid, 20°C, sweet smell, no powder visible Which option correctly compares the properties before and after?
8. A student builds an instant cold pack using ammonium nitrate (NH₄NO₃) in one pouch and water in a separate inner pouch. When squeezed, the inner pouch breaks and the contents mix. Why does the cold pack get cold after activation?​
9. A helmet must meet these criteria: peak force below 500 N, weight less than 300 g, cost under $30. Design B results: 550 N, 200 g, $25. Based on the test data, is Design B acceptable, and why?
10. A student accidentally builds an instant hot pack by sealing calcium chloride and water together in the same pouch with no inner barrier. The pack warms up immediately during storage and is cool when the student tries to use it later. What design feature was missing that would have prevented this problem?
11. Two substances are modeled at the particle level. Substance A is carbon monoxide, $\mathrm{CO}$ (carbon = black, oxygen = red). Substance B is carbon dioxide, $\mathrm{CO_2}$ (carbon = black, oxygen = red). Which statement best describes a pattern that explains why they are different substances?
12. A student uses a field-line model to compare two locations around the same source. At location X the field lines are very dense; at location Y they are spread out. What is the best conclusion about the forces on the same test object placed at X versus Y?
13. A metal spoon is left in a freezer at about 0°C. Later, the spoon is warmed in a cup of hot water at about 80°C. How does the motion of the particles in the spoon change as its temperature increases from 0°C to 80°C?
14. A student pushes a shopping cart forward across a smooth floor. While the student is pushing, the cart speeds up. Which statement best connects the force to the change in kinetic energy?
15. Three carts all move at the same constant speed of $v=3\ \text{m/s}$. If you extend the pattern, what kinetic energy would you expect for a cart with mass $7\ \text{kg}$ at the same speed?
16. A student wants their reusable sodium acetate heat pack to be used again after it has crystallized and cooled. Which method best "resets" the pack so it can release heat again later?
17. A fiber-optic cable carries internet signals across a city. It sends pulses of infrared light through glass. What information is primarily being transmitted in the fiber, and how do the waves carry it?​​​
18. Design Challenge (Hand Warmer): Students are designing a reusable hand warmer to use at an outdoor football game when the air temperature is about $5^\circ\text{C}$. The device should release thermal energy to keep hands warm. Which option is the best measurable performance criterion for this hand warmer?
19. A student can rub different rods (plastic, glass, and rubber) with the same cloth and then bring each rod near small paper pieces to see how strongly they attract. What is the best investigable question about factors affecting electric force in this situation?
20. A foam cup (0.5 cm walls) with a loose plastic lid (not sealed) was tested with hot water at 70°C in a 22°C room. Temperatures were measured hourly: - 0 hr: 70°C - 1 hr: 58°C - 2 hr: 48°C - 3 hr: 40°C Criterion: Maintain ≥60°C for 3 hours. Which specific measurement shows the first time the cup fails the criterion?

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