Practice Test 3 - 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 pendulum bob swings back and forth. Consider three positions: Position A is the left highest point, Position B is the lowest point, and Position C is the right highest point. Which statement correctly identifies where gravitational potential energy is minimum and what that implies about stable equilibrium?
2. A student compares two setups to see what changes the force the most. Setup 1: A strong magnet at 6 cm pulls 2 paper clips. Setup 2: The same strong magnet at 2 cm pulls 10 paper clips. Which factor caused the force to increase from Setup 1 to Setup 2?
3. A student investigates: Does temperature difference affect cooling rate? They pour 250 mL of water into the same insulated cup at three different starting temperatures: 60°C, 70°C, and 80°C. The room temperature stays the same. They record the temperature every minute for 15 minutes and calculate cooling rate in °C/min. Which pair correctly matches the independent and dependent variables?
4. During a cart collision, sensors report $F_{A\text{-on-}B}=+8\,\text{N}$ (to the right) and $F_{B\text{-on-}A}=-8\,\text{N}$ (to the left) at the same moment. Which conclusion is correct?
5. Which feature best distinguishes a molecular substance (like water vapor, $\mathrm{H_2O}$) from an extended crystal structure (like diamond or salt)?​
6. A person of mass $m$ climbs stairs from the first floor at $h=0\,\text{m}$ to the second floor at $h=3\,\text{m}$ and then to the third floor at $h=6\,\text{m}$. How does the person's gravitational potential energy change from the first floor to the third floor (in terms of $m$ and taking $g\approx 10\,\text{m/s}^2$)?
7. A student investigates motion using a cart and a ramp. The investigation question is: How does the mass of the cart affect its speed at the bottom of the ramp? The student plans to add different masses (like 0 g, 200 g, 400 g) to the same cart and release it from the same starting point. Which variable is the independent variable in this investigation?
8. A student notices that WiFi usually works through walls, but a TV remote control (infrared light) often fails if something blocks the direct path. Which wave property best explains why WiFi is more likely to work through walls?
9. Design challenge: Design a cold pack that absorbs thermal energy to cool an injury. Criteria: $0$–$5^\circ\text{C}$, lasts 30+ minutes, safe on skin, flexible. Constraints: affordable and must be school-safe. Which option shows the best way to make the duration requirement measurable?​
10. Cold drink cooler design challenge: You are designing a cooler for an outdoor event lasting 4 hours in 30°C weather. It must keep the drinks at or below 10°C. It must hold 12 standard cans. The budget is $50. It must be portable (handles or wheels), durable for repeated use, and you can use foam, plastic, and ice/ice packs. Which option best identifies the constraints (limits) for this design?
11. A ball is thrown straight upward. It slows down as it rises, stops for an instant at the top, and then speeds up downward. What role does gravity play in this motion?
12. A bicycle left out in the rain develops a rough, reddish coating on the metal parts over time. Which evidence most strongly indicates this is a chemical change?
13. Two carts are tested at the same speeds but have different masses. If you graph kinetic energy (J) vs speed (m/s), which statement is correct about the two curves?
14. Steel wool is placed in a sealed jar (a closed system) and allowed to rust. The jar is weighed on a balance. Mass data (g): - Before: sealed jar + steel wool + air inside = 100 g - After: sealed jar + rust (iron oxide) + remaining air inside = 100 g Why does the total mass remain constant even though the steel wool changes into rust?
15. A student made a cold box with thin metal walls, no lid, and a black exterior. In a test, all the ice melted in 2 hours (complete failure). The student concludes that conduction through the metal, convection through the open top, and radiation from sunlight are all problems. Which set of improvements best addresses all three heat transfer pathways?​
16. A student investigates: How does surface type affect how far a toy car rolls? The student uses the same toy car and the same starting push each time, and tests on tile, carpet, and sandpaper. Which set of variables should be controlled (kept the same) to make it a fair test?
17. Wave: light traveling through air approaches the surface of a swimming pool at an angle. Medium change: air to water. Water is optically denser than air, so light travels slower in water. What is the most likely set of behaviors when the light reaches the air–water boundary?
18. A student is comparing materials for the walls of a cooler to minimize heat gain by conduction. Which wall material is the best insulator (best at slowing conduction)?
19. A roller coaster cart moves through these heights above the ground: bottom ($h=0\text{ m}$) \u2192 top of a hill ($h=20\text{ m}$) \u2192 halfway down ($h=10\text{ m}$) \u2192 bottom again ($h=0\text{ m}$). At which position is the cart's gravitational potential energy greatest?
20. A satellite moves in an elliptical orbit around Earth. Gravity (a non-contact force) always pulls the satellite toward Earth. When the satellite moves closer to Earth, it speeds up. What best explains this change in speed in terms of work and energy?

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