Grade 8 Science: 10 Free Practice Questions

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: It is the same, because the height dropped is unchanged
Gravitational potential energy depends only on mass and the vertical height dropped, so the same drop releases the same energy however long the slope is. Choosing greater because the journey is longer is the error; a gentler slope spreads the same transfer over more distance, which is exactly why ramps feel easier.

Answer: Vary only the pitch; keep the air and distance fixed
The fair test changes only the pitch and keeps everything else, the air and the distance, constant, while measuring the travel time. The other options change more than one thing at once: loudness and temperature, distance and loudness, or pitch and material. Then you could not tell which change caused the result. A fair test changes one variable, holds the others constant and measures one outcome.

Answer: Real use may include conditions the lab test left out
A lab test checks only the conditions the team chose, such as one drop height. Real users may drop the product on rough ground, in the cold, or many times over. Passing one test is good evidence but it does not prove perfection. More tests under realistic conditions are needed before sale. Passing a test has no effect on cost.

Answer: Same temperature, but the 5 kg block has more thermal energy
Temperature is given as 80 degrees for both, so that part is settled, but thermal energy also counts how many particles are vibrating, and the heavier block has five times as many. The tempting error treats a bigger mass as a higher temperature, which it is not; they are separate ideas.

Answer: Wave R
Wave R is the fastest. Speed equals frequency times wavelength. Wave P has 6 × 2 = 12 m/s, Wave Q has 20 × 0.5 = 10 m/s, Wave R has 3 × 5 = 15 m/s and Wave S has 40 × 0.25 = 10 m/s. If you picked Wave S for its high frequency, you ignored the wavelength. Always multiply both quantities before comparing speeds.

Answer: F2
Check each design against all three limits. F2 costs $18, takes 9 minutes and cleans 93%, so it passes. F1 cleans only 78%. F3 cleans 97% but costs $26. F4 cleans 91% but takes 14 minutes. Only one design passes every requirement, even though F3 is best on cleaning and F1 is cheapest.

Answer: Most energy is lost as heat at each step
Only a small part of the energy at one level, roughly 10 percent, is stored in the bodies of the next level. The rest is used for life processes and released as heat. After four or five steps too little energy remains to support another group of organisms. Energy is never created at higher levels.

Answer: 20 years
The supply is fixed, so the time it lasts equals the supply divided by the yearly use. Doubling the use halves the time: 40 divided by 2 is 20 years. If you chose 80, you doubled the time when the use doubled, but a faster rate of use runs the supply down sooner. Remember the estimate also changes if new reserves are found.

Answer: A chemical reaction occurred because the properties changed
A chemical reaction occurred. The color changed and the powder no longer fizzes with acid, so a new substance with different properties was made. The mass fell because a gas escaped from the open tube. Staying a solid does not prove nothing happened; a new substance can also be a solid. When several properties change at once, a new substance has formed.