Grade 8 Science: 10 Free Practice Questions

Answer: It makes clean power but floods habitat and blocks fish
A trade-off means a benefit comes with a cost. A dam turns flowing water into electricity without burning fuel, which is a benefit, but the reservoir floods land and the dam can block migrating fish. Dams do change rivers, they do not burn fuel, and water continues downstream. Evaluating a solution means weighing both its benefits and costs against stated criteria.

Answer: Cup A has more thermal energy; the temperatures are equal
Both cups are at 60 °C, so the particles have the same average kinetic energy, but cup A has five times as many particles, so it holds more total thermal energy. If you chose that they have the same thermal energy, you treated temperature and thermal energy as the same thing. If you chose that A is hotter, you confused amount with temperature. Thermal energy depends on both temperature and quantity.

Answer: Wave A has the greater amplitude and the lower frequency
Wave A rises 2 cm while Wave B rises only 1 cm, so A has the greater amplitude. Wave A's wavelength is 8 cm and Wave B's is 4 cm. At the same speed, the longer wavelength means fewer waves per second, so A has the lower frequency. If you chose higher frequency for A, you linked the bigger wave with more waves per second, but it is the shorter wave that repeats more often.

Answer: 10 from each parent; 20 in each body cell
Sex cells carry half of the parent's chromosomes, so each parent gives 10. The egg and sperm join to restore the full number of 20, and 20 is the count in the fertilized egg. Mitosis then copies the full set into every new cell, so each body cell has 20. Chromosome numbers do not add up to 40 in body cells.

Answer: Foam A
Check each material against all three limits. Foam A has a mass of 120 g, costs $6 and absorbs 82 percent, so it passes. Foam B is light and cheap but absorbs only 75 percent. Gel absorbs 91 percent but is 210 g and costs $9. Cork is cheap but heavy at 180 g and absorbs only 60 percent. Only one material passes every test.

Answer: The Moon's gravitational pull
The Moon's gravity pulls on Earth, and the ocean water facing the Moon is pulled the most, creating a bulge of high tide. Earth's spin carries coasts through the bulges, so most places have two high tides a day. Wind makes waves, not tides, and sunlight heats water but does not raise it. If you chose the Sun, note that its gravity matters much less.

Answer: Still rising, but more slowly lately
The total rose by 30 thousand from 2014 to 2016 and again from 2016 to 2018, then by 20 and then by 10. The line keeps going up, but each step is smaller, so growth is slowing. The total never goes down. Students who see the line flatten sometimes say it is decreasing, but the quantity is still increasing, just by less each time.

Answer: M2
M1 gives 130 out of 200 J, which is 65%. M2 gives 175 out of 250 J, which is 70%. M3 gives 220 out of 400 J, which is 55%. M2 is the most efficient. M3 produces the most useful energy, but it also takes in the most, so its larger output does not mean it wastes less.

Answer: Homes and power plants
Farming uses 80 billion liters per day. Homes use 20 and power plants use 60, and 20 + 60 = 80, so those two together match farming. Factories (40) plus homes (20) give only 60, and factories plus power plants give 100. Test each pair by adding the bar values instead of estimating from the bar heights.

Answer: Desert
Deserts receive very little rain, so plants and animals there have adaptations for saving water, such as the thick stems of cacti. Without clouds or moisture to hold heat, temperatures swing widely between day and night. A tropical rain forest is very wet, the taiga is cold with evergreen forests, and a grassland has moderate rainfall.