Practice Test 12 - 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 field model uses line density (lines closer together) to show a stronger field. Two points, A and B, are in the gravitational field around Earth. Point A is closer to Earth's surface than point B. What does the model predict about the gravitational force on the same object placed at A versus B?
2. A gas is easy to compress (squeeze into a smaller volume). Which particle-level reason best explains this?
3. A class wants to collect data to show how net force affects motion for the same cart. They have a spring scale (to measure pulling force) and a motion sensor (to measure acceleration). Which plan would best test the relationship between $F_{\text{net}}$ and acceleration while keeping the investigation fair?
4. During an earthquake, a seismograph shows small-amplitude shaking for Event A and large-amplitude shaking for Event B. Which conclusion about energy is most accurate?​
5. A student tested a homemade cooler for keeping ice from melting. Design: 4 cm foam insulation on all sides, sealed lid, white exterior paint to reflect sunlight, and duct-taped seams. Performance test: Started with 1000 g of ice. After 6 hours, 850 g of ice remained (150 g melted). The cooler held 12 drinks. Total cost was $\45$. Criteria: At least 800 g of ice remaining after 6 hours, hold 12 drinks, and cost $<\$50$. Which evaluation is correct?
6. A bike helmet is designed to protect a rider's head in a fall. Which change would best help by distributing the force over a larger area and reducing pressure on the skull?
7. Two particle-level models are shown. Substance A: water, H₂O (H = white, O = red) shown as separate molecules. Substance B: table salt, NaCl (Na = purple, Cl = green) shown as a repeating crystal pattern. Which observable structural feature best distinguishes Substance B from Substance A in the models?
8. A student claims, "Gravity is always attractive—it only pulls objects together and never pushes them apart." Which set of observations best supports this claim? Consider everyday evidence (like objects falling), space evidence (like orbits), and Earth evidence (like tides).
9. Three 200 g samples (water, oil, and sand) are each heated to 80°C and then left to cool for 10 minutes in the same room using identical containers. After 10 minutes their temperatures are: water 65°C, oil 58°C, sand 52°C. Which material cooled the fastest over the 10 minutes?​​​
10. Earth can be modeled as a mass that creates a gravitational field in the space around it. What does a gravitational field model (field lines pointing toward Earth) explain about why objects fall?
11. A pulse travels along a rope toward a boundary. The student observes that the reflected pulse comes back upside down (inverted). Which boundary condition most likely caused this inversion?
12. A student compares diamond and graphite (both made of carbon). Diamond scratches glass easily, but graphite rubs off on paper and feels soft. Which particle-level feature best explains the difference in hardness?
13. A moving billiard ball rolls toward an identical ball that is initially at rest. They collide, and after the collision the first ball slows down while the second ball starts moving. What is the main way energy is transferred between the balls during the collision?
14. A student makes a KE (J) vs mass (kg) graph for an object moving at constant speed. The line goes through the origin and has a slope of $12.5\ \text{J/kg}$. What constant speed was the object moving at?
15. A ball is dropped from rest from a balcony at height $h=8\,\text{m}$ above the ground (ground is the reference level, $h=0$). As the ball falls toward the ground, what happens to its gravitational potential energy?
16. To visualize a magnetic field, a student places a sheet of paper over a bar magnet and sprinkles iron filings on top. The filings form curved lines that go from one end of the magnet to the other, and the filings are densest near the ends. What does this investigation demonstrate about the magnetic field?
17. A music recording is duplicated several times. An analog cassette copy adds a little hiss and distortion each time it is copied (copy 1 to copy 2 to copy 3 to copy 4). A digital audio file is copied from one device to another by copying 0s and 1s. After 4 generations of copying, which statement best compares the sound quality?
18. A water wave (ripples) moves across a pond and reaches a floating barrier made of stiff plastic. The barrier is not very absorptive, but it blocks the water motion. What is the best prediction?
19. A 1 kg ball hits a very massive concrete wall and bounces back. The wall does not noticeably move. Which statement best describes the forces during the collision?
20. A phone company sends a signal 100 km through a cable that adds noise of about $\pm 0.3\text{ V}$. An analog audio signal is a continuous wave that ranges from $-1\text{ V}$ to $+1\text{ V}$, so the noise makes the wave arrive "wiggly" and changed. A digital signal uses only two voltage levels: $0\text{ V}$ for 0 and $5\text{ V}$ for 1. After the same trip, the digital signal arrives as $0\pm 0.3\text{ V}$ and $5\pm 0.3\text{ V}$. The receiver decides "0" if the voltage is below $2.5\text{ V}$ and "1" if it is above $2.5\text{ V}$. Why will the digital signal usually stay clearer than the analog signal over this distance?

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