Grade 8 Science: 10 Free Practice Questions

Answer: Zero while steady, then leftward while braking
A steady speed in a straight line means balanced forces and zero net force, because nothing about the velocity is changing. Braking slows the car, a change in velocity opposite to the motion, so the net force points left. Believing a moving car needs a forward net force is the misconception this item targets.

Answer: Weights should be chosen from the criteria before scoring
Weights state how much each criterion matters to the client, so they should be set from the problem definition before any scores are known. Adjusting them afterward to favor one design makes the matrix a justification instead of a fair comparison. Weights need not be equal, matrices can use them, and changing them does not make scores identical.

Answer: Solid
The sample is a solid. In a solid the particles are packed tightly in a regular pattern and can only vibrate in place, so a solid keeps its own shape and volume. The diagram shows touching particles in neat rows and columns. If you chose liquid, you noticed the particles are close, but liquid particles are close and jumbled so they can slide past each other. Check the pattern first: tight and ordered means solid.

Answer: 200 N upward
The net force is 200 N upward. The engine pushes up with 500 N and weight pulls down with 300 N, and opposing forces are subtracted: 500 N − 300 N = 200 N, in the direction of the larger force. If you chose 800 N, you added them. If you chose 200 N downward, you took the direction of the smaller force. The net force always points the way the larger force acts.

Answer: The total stays the same, though energy changes form
Conservation means the total never changes: energy moves between stores and spreads out, but none is made or lost. The everyday meaning of conserving energy, as in saving electricity, is the tempting answer and a different idea altogether. In physics it is a strict accounting rule, and every joule must balance.

Answer: A measurement or equipment error occurred.
Mass cannot be created, and a sealed flask cannot gain anything from outside, so a 2-gram rise points to an error - a mis-read balance, something resting against the flask, or condensation on the outside. Warming does not change mass either, only volume and pressure. When a result contradicts a well-established law, suspect the measurement before overturning the law.

Answer: V3
The V3 bar is the tallest, at 95 degrees C. V4 reached 90, V2 reached 75 and V1 reached 60. The oven improved from V1 to V3 and then dropped slightly in V4. This shows that a later version is not always better, and that each new version must be tested to find out.

Answer: Hydropower
First keep only the sources marked Yes for working at night: coal, natural gas and hydropower. Of these, hydropower releases 24 g of CO2 per kWh, far below natural gas at 500 g and coal at 1000 g. Wind has the lowest CO2 overall, but it is marked Sometimes, so it fails the night requirement. Apply the filter first and then compare.

Answer: Stopped on a distance graph, steady speed on a speed graph
A flat line always means the quantity on the vertical axis is unchanging. If that quantity is distance, the object is not moving; if it is speed, the object keeps moving at the same rate. Treating the two graphs as interchangeable is the most common graph error in this topic, so read the vertical axis label before you read the line.

Answer: F3
Look down the Water cleaned column. F3 cleaned 97%, F2 cleaned 93%, F4 cleaned 91% and F1 cleaned only 78%. So F3 did the best job on that one measure. Notice that F3 is also the most expensive filter, which shows why a team must look at every column and not just one before choosing a final design.