Practice Test 6 - 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 car is stopped at a red light. Which statement correctly uses a reference frame to describe the car as being at rest?​​
2. A student stirs a spoonful of sugar into a glass of water. After a minute, the sugar crystals are no longer visible, but the water tastes sweet everywhere. Macroscopic level: crystals "disappear" and the solution stays clear. Particle level: sugar is made of sugar molecules. What particle-level change best explains these macroscopic observations?
3. A $3\text{ kg}$ backpack is on a ledge $2\text{ m}$ above the ground. Using $g \approx 10\text{ m/s}^2$, which expression correctly gives its gravitational potential energy?
4. A ball is thrown horizontally. If gravity could be "turned off" right after the throw (ignore air resistance), what would the ball do after leaving the thrower's hand?
5. A student heats 100 g of water from $20^\circ\text{C}$ to $80^\circ\text{C}$ in 2 minutes using a burner with constant power. If the student heats 300 g of water from $20^\circ\text{C}$ to $80^\circ\text{C}$ using the same burner, about how long should it take (assuming similar conditions)?​
6. A student mixes a blue sports drink (blue liquid, clear, 6°C) with a yellow sports drink (yellow liquid, clear, 6°C) in the same cup. After mixing, the liquid is green and still clear, with no bubbles and no noticeable temperature change. Which property definitely changed?
7. A cooler was tested to keep ice from melting. Current design: 2 cm foam walls, the lid is opened often to check the ice, and the exterior is dark blue. Test result: started with 1000 g of ice and had 720 g left after 6 hours (280 g melted). The success criterion is $\le 200$ g melted in 6 hours. Which change should be made first to reduce heat transfer by convection?
8. Particle model for rusting iron (simplified) (colors: Fe = gray, O = red). Reactants (before): 4 atoms Fe and 3 molecules O₂ - Fe: Fe Fe Fe Fe - O₂: (O–O), (O–O), (O–O) Products (after): 2 formula units Fe₂O₃ - Fe₂O₃: (Fe Fe O O O) and (Fe Fe O O O) Which counting is correct, and are atoms conserved?
9. A student accidentally builds a "cold pack" by putting calcium chloride (CaCl₂) in one compartment and water in the other. When activated, it warms instead of cooling. Which change would correctly turn the device into a cold pack that absorbs thermal energy when activated?​
10. In a collision, a moving cart pushes on a stationary cart for a short time while they are in contact. Which statement best describes how the kinetic energy is transferred from one cart to the other?​
11. A model shows methane burning: Before: 1 methane molecule (CH₄) and 2 oxygen molecules (O=O and O=O). After: 1 carbon dioxide molecule (O=C=O) and 2 water molecules (H–O–H and H–O–H). How many oxygen atoms are shown before and after the reaction?
12. A diagram model shows particles in Sample A packed closely in a fixed, repeating pattern. In Sample B, the same particles are still close together but are in a more random arrangement and can slide past each other. Which macroscopic observation is most consistent with Sample A changing to Sample B?​
13. A cooler test started with 1000 g of ice at $0^\circ\text{C}$ in a $25^\circ\text{C}$ room. Ice mass remaining was: 0 hr: 1000 g 2 hr: 920 g 4 hr: 840 g 6 hr: 760 g Criterion: by 6 hours, no more than 200 g may melt. How many grams of ice melted by 6 hours, and does that meet the criterion?
14. A cold pack is made by dissolving 20 g of ammonium nitrate in 80 mL of water inside a sealed plastic pouch. Success criteria: cool to between 0°C and 5°C within 3 minutes and stay below 10°C for 20 minutes. Test results: starting at 22°C, the lowest temperature reached was 15°C at 2 minutes, and it warmed back to 18°C by 10 minutes. What modification would best help the cold pack meet the 0–5°C temperature criterion?
15. A student is improving a hot pack design. Criterion: Reach $40$–$50^\circ\text{C}$ and maintain that range for at least 2 hours. Test procedure: Measure temperature every 15 minutes. Data (time | temperature): 0 min 22°C; 15 35°C; 30 41°C; 45 44°C; 60 43°C; 75 41°C; 90 39°C; 105 37°C; 120 35°C. Which change most directly targets the criterion the design failed to meet?​
16. A student heats a piece of wax until it becomes a liquid. Macroscopically, the wax changes from a solid that holds its shape to a liquid that can be poured. The thermometer shows the wax warming during heating. Which statement best connects BOTH macroscopic observations (state change and temperature increase) to particle-level changes?​
17. On Earth, a 2 kg object has weight 20 N. If you keep the same planet and double the object's mass to 4 kg, what happens to the gravitational force (weight)?
18. A toy car rolls down a ramp and then across a rough carpet until it stops. Before it reaches the carpet, it is moving fast. After it stops, the carpet feels slightly warmer in the path where the car rolled. Which evidence best shows that the car's kinetic energy decreased and was transferred to thermal energy?
19. A student places a capped bottle of soda in the refrigerator for an hour. When opened, it still fizzes, but the fizzing is less vigorous than when the soda was warm. Which particle-level explanation best connects the cooler temperature to the reduced fizzing?
20. A tide-prediction model uses the Moon's gravitational pull to predict when high tides should occur at a certain beach. Over a month, the predicted high-tide times are usually within about 30 minutes of the observed high-tide times. What does this match between prediction and observation best support?

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