Practice Test 8 - 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 graphs kinetic energy (J) vs speed (m/s) for a cart while keeping mass constant. Which statement correctly describes what happens to the steepness (slope) of the curve as speed increases?
2. A wave's amplitude is the maximum displacement from its resting position. If the amplitude of a wave increases, what happens to the energy the wave can transfer to objects in its path?
3. A small piece of steel wool is observed before and after being left in a damp paper towel overnight. Before: shiny gray metal strands, dry, no odor, room temperature. After: strands are reddish-brown in spots, look dull, and feel slightly rougher. Which property change is the clearest evidence that the steel wool reacted with the air/water?
4. A student tests which material insulates best by wrapping cups with foam, plastic, and fiberglass. The student also uses different thicknesses of each material (thin foam, thick plastic, medium fiberglass). What is the main problem with this plan?
5. A spring on a table is compressed and then released. Consider three positions of the spring: (1) relaxed (not compressed), (2) slightly compressed, (3) more compressed. Which statement best describes the direction of the spring force and how elastic potential energy (PE) changes with compression?
6. A city is choosing packaging for milk served in school lunches. The city has a tight budget and must ship lunches across town every day. Here are the options: - Plastic carton: low cost, lightweight, waterproof, protects milk well, but does not biodegrade. - Paper carton: made from renewable trees, biodegradable, but can leak if the lining fails and is slightly more expensive. - Glass bottle: recyclable and does not react with food, but heavy and breakable, increasing shipping cost and safety concerns. Which trade-off must the city balance most when choosing the packaging?
7. A continuous wave travels down a rope toward a loose end (free end). The incident and reflected waves overlap. What pattern forms near the end, and what is always true right at the free end?
8. A student charges a balloon by rubbing it on hair, then slowly moves it away from a pile of tiny paper pieces. They want to measure how electric force changes with distance. What is the best dependent variable (what they should measure/observe) to show force strength in this setup?
9. Two identical flower pots are placed at the same height of 2 m above the ground (ground is the reference level). Pot A has mass 2 kg and Pot B has mass 4 kg. Using $g \approx 10\ \text{m/s}^2$, how does Pot B's gravitational potential energy compare to Pot A's?
10. A student puts 50.0 g of vinegar into a flask and 5.0 g of baking soda into a balloon. The balloon is stretched over the flask opening so the system is closed (no gas can escape). The mass of the entire setup (flask + vinegar + balloon + baking soda) is 155.2 g before mixing. The student tips the baking soda into the vinegar; the balloon inflates with CO$_2$ gas. After the reaction stops, the mass of the entire setup is 155.2 g (±0.1 g). Which statement best uses this evidence to support conservation of mass?
11. A student rubs their hands together for 20 seconds. Before rubbing, their hands feel cool. After rubbing, their hands feel warmer, and a soft rubbing sound is heard. Which conclusion is best supported by these observations?
12. A phone call is sent 100 km through a cable where random noise of about $\pm 0.3\,\text{V}$ gets added. An analog version of the voice uses a continuous signal that ranges around $\pm 1\,\text{V}$, so the noise changes the wave shape as it travels. A digital version sends bits using $0\,\text{V}$ for 0 and $5\,\text{V}$ for 1, and 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 call usually sound clearer after 100 km?
13. A student leaves an ice cube on a plate at room temperature. After 10 minutes, the ice cube has turned into a puddle of liquid water that can flow across the plate. Which particle-level change best explains this macroscopic change (solid to liquid and flowing)?
14. A student mixes two substances and records observations in this table: Property | Reactants (before) | Products (after) - Appearance | white powder + clear liquid | foamy liquid with many bubbles - Temperature (by touch) | room temperature | feels cooler - Gas/odor | no bubbling | bubbling/fizzing for about 30 seconds Based on the property comparison, what is the best conclusion?
15. A student mixes two clear liquids in a beaker. Before mixing: both liquids are clear and colorless. After mixing: the mixture turns cloudy and a solid settles to the bottom (a new solid forms). No pieces were added after mixing. Which observation is the best evidence that a chemical reaction occurred?
16. A student places a cold metal can (5°C) into a cooler with warm water (40°C). After a while, the can warms up and the water cools slightly. Which choice best traces the pathway and mechanism of energy transfer between the water and the can?
17. A horizontal spring is attached to a wall. The spring is at its relaxed length at Position R, and it can be compressed to Position C1 (compressed $5\,\text{cm}$) or Position C2 (compressed $10\,\text{cm}$). The spring force on the attached block points away from the wall (toward the relaxed length) when the spring is compressed. Which statement is correct about force direction and elastic potential energy (PE)?
18. A student hits a baseball with a bat. During the brief moment the bat and ball are in contact, the ball speeds off in a new direction and the batter feels the bat "sting" in their hands. Which pair of forces is the Newton's Third Law action-reaction pair during the collision?
19. A person of mass $m$ climbs stairs from the first floor (Position A, $h=0\text{ m}$) to the second floor (Position B, $h=3\text{ m}$) to the third floor (Position C, $h=6\text{ m}$). How does the person's gravitational potential energy change from A to C (relative to A)?
20. On a displacement graph, the wave's maximum displacement is $-4\text{ cm}$ (the lowest trough) and the equilibrium line is at $0\text{ cm}$. What is the amplitude of the wave?

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