CST Science Pre-test Prep Test 8th Graders

The galaxies pictured above would best be classified as spiral galaxies because they exhibit a distinct spiral structure with arms that extend outwards from a central bulge. This classification is based on their visual appearance, which resembles the characteristic spiral shape commonly associated with spiral galaxies. Barred galaxies typically have a bar-like structure running through their central region, while irregular galaxies lack a defined shape or structure. Symmetrical galaxies is a vague term that does not provide enough information to accurately classify the galaxies in the picture.

A galaxy is best described as a cluster of billions of stars. Galaxies are massive systems that contain a vast number of stars, along with other celestial bodies such as planets, nebulae, and black holes. The number of stars in a galaxy can vary, but on average, there are billions of stars within a single galaxy. This makes the option "billions of stars" the most accurate description of a galaxy.

Metals are the best conductors of electricity among the given options. This is because metals have a high number of free electrons that are mobile and can easily carry electric charge. The delocalized electrons in metals are not strongly bound to specific atoms, allowing them to move freely and conduct electricity efficiently. In contrast, nonmetals, semimetals, and noble gases have fewer free electrons or lack them altogether, making them poor conductors of electricity.

The average speed of the bicycle is given as 2 m/s. To find the time required to travel a distance of 100 m, we can use the formula time = distance/speed. Plugging in the values, we get time = 100 m / 2 m/s = 50 s. Therefore, the correct answer is 50 s.

The cart will move as if it were acted on by a single force with a magnitude of 50 N because the forces applied by the two students are in opposite directions. The net force acting on the cart is equal to the difference between the two forces, which is 200 N - 150 N = 50 N.

C4H12O6, also known as glucose, is the most likely compound to be part of living organisms. Glucose is a simple sugar and a key source of energy in biological systems. It is a primary fuel for cellular respiration and is used in various metabolic processes. Glucose is a fundamental component of carbohydrates and is essential for the functioning of living organisms, making it the most likely compound to be found in them.

The most appropriate unit of measurement to express the distance between the Milky Way galaxy and other galaxies is the light-year. A light-year is the distance that light travels in one year, which is approximately 9.46 trillion kilometers. Since the distances between galaxies are extremely vast, using kilometers or meters would be impractical. The light-year provides a more convenient and meaningful measure of these enormous distances in the context of astronomical observations.

Electrons are found farthest from the center of an atom. They exist in energy levels or orbitals surrounding the nucleus. Electrons have a negative charge and are much smaller and lighter compared to protons and neutrons, which are located in the nucleus. The electrons' position in the atom is not fixed but rather exists in a cloud-like region, making them the farthest from the center.

In most chemical reactions, heat energy is released or absorbed. This is because chemical reactions involve the breaking and forming of chemical bonds, which requires energy. When bonds are broken, energy is absorbed, and when new bonds are formed, energy is released. The release or absorption of heat energy is a common indicator of a chemical reaction taking place. Light energy, electrical energy, and sound energy can also be involved in certain chemical reactions, but heat energy is the most commonly released or absorbed form of energy.

The density of a substance is defined as its mass divided by its volume. In this question, we are given the mass of the iron cube (64 g) and the volume of water it displaces (8 mL). To find the density, we divide the mass by the volume: 64 g / 8 mL = 8 g / mL. Therefore, the correct answer is 8 g / mL.

The student is using density to classify the cubes. Density is a property that describes how much mass is contained in a given volume. If a cube has a lower density than water, it will float, and if it has a higher density, it will sink. Therefore, by observing whether the cubes float or sink in water, the student can determine their relative densities and classify them accordingly.

Iron oxide is a compound that forms when iron metal reacts with oxygen in the air. The chemical symbol for iron is Fe, while the chemical symbol for oxygen is O. Therefore, the correct answer is Fe and O.

As the ball falls, the force of gravity pulls it downward, while the force of air resistance acts in the opposite direction. Initially, the force of gravity is greater than the force of air resistance, causing the ball to accelerate. However, as the ball gains speed, the force of air resistance also increases. Eventually, a point is reached where the force of air resistance becomes equal to the force of gravity. At this point, the ball stops accelerating and falls at a constant speed, known as terminal velocity. Therefore, the correct answer is that the ball will fall at a constant speed.

An atom is described as a core of protons and neutrons surrounded by electrons. This is because an atom consists of a nucleus at its core, which contains protons (positively charged particles) and neutrons (neutral particles). The protons and neutrons are tightly packed together in the nucleus. Surrounding the nucleus are electrons (negatively charged particles) that orbit in specific energy levels or shells. Therefore, the correct answer is a core of protons and neutrons surrounded by electrons.

Carbon is the best element to combine with itself and hydrogen to form large molecules because it has a unique ability to form strong covalent bonds with other carbon atoms, resulting in the formation of long chains and complex structures. This property of carbon is known as catenation, and it allows for the formation of diverse organic compounds, including carbohydrates, lipids, proteins, and nucleic acids, which are essential for life. Sodium, lithium, and sulfur do not possess this ability to the same extent as carbon, making carbon the correct answer.

The elements sulfur, nitrogen, phosphorus, and bromine have in common that they are nonmetals. Nonmetals are a group of elements that do not exhibit typical metallic characteristics such as being shiny, malleable, or good conductors of heat and electricity. Instead, nonmetals tend to be brittle, dull, and poor conductors. Sulfur, nitrogen, phosphorus, and bromine all fall into this category, making them nonmetals.

When magnesium metal is burned in the presence of oxygen, a chemical reaction occurs and magnesium oxide is formed. In a compound, the elements are chemically bonded together in a fixed ratio. Magnesium oxide is composed of one magnesium atom bonded to one oxygen atom, forming a stable compound with distinct properties different from those of the individual elements. Therefore, the correct answer is that magnesium oxide is a compound.

When water turns to ice, the arrangement of the molecules changes. In the liquid state, the water molecules are constantly moving and have enough energy to overcome the attractive forces between them. However, as the temperature decreases, the molecules slow down and the attractive forces become stronger. This causes the water molecules to arrange themselves in a regular pattern, forming a solid structure known as ice. Therefore, the correct answer is that the arrangement of the molecules changes.

Given that the object is composed mainly of ice and is orbiting the Sun in an elliptical path, it is most likely a comet. Comets are composed of ice, rock, and dust and they follow elliptical orbits around the Sun. They often have a visible coma (a glowing atmosphere) and a tail when they approach the Sun due to the heat causing the ice to vaporize and release gas and dust. Planets, asteroids, and meteors do not typically have a composition of ice or exhibit the characteristics of a comet.

The correct answer is 40 m / s north because velocity is a vector quantity that includes both magnitude (40 m/s) and direction (north). The other options either lack direction (40) or provide only magnitude without specifying the direction (40 m north, 40 m/s).

In a gas, atoms have high kinetic energy and are in constant motion, colliding frequently with each other. These collisions are relatively independent, meaning that they do not have a strong attraction or bond to each other. This is in contrast to a solid or crystal, where atoms are tightly packed and have strong interactions, or a liquid where atoms are still close together but have more freedom of movement compared to a solid. Therefore, atoms that collide frequently and independently are most likely in a gas.

Carbon bonds in many ways with itself to form chains. This characteristic of carbon allows it to form the backbone of organic molecules, which are the building blocks of life. Carbon can form single, double, and triple bonds with other carbon atoms, as well as form bonds with other elements such as hydrogen, oxygen, nitrogen, and sulfur. This versatility in bonding allows carbon to create a wide variety of complex and diverse molecules, including carbohydrates, lipids, proteins, and nucleic acids, which are essential for the structure and function of living organisms.

Increasing the mass of the box would require additional force to produce the same results because according to Newton's second law of motion, force is directly proportional to mass. Therefore, increasing the mass would increase the force required to accelerate the box.

The characteristic of motion that could change without changing the velocity of an object is the position. Velocity is a vector quantity that includes both speed and direction. However, if only the position of an object changes, while the speed and direction remain constant, the velocity will remain the same. This means that the object can move to a different location but still have the same velocity.

The answer is 2m3 of bricks. This is because the density of bricks is much higher than the density of air. Therefore, even though the volume of 2m3 of bricks is smaller than the volume of air, the mass of the bricks will be greater.

Metals tend to have greater conductivity and higher melting points than nonmetals. This is because metals have a sea of delocalized electrons that can easily move and carry electric charge, making them good conductors of electricity. Nonmetals, on the other hand, have fewer free electrons and therefore have lower conductivity. Additionally, metals have strong metallic bonds, which require high temperatures to break, resulting in higher melting points compared to nonmetals.

Moons, planets, and comets are all celestial objects that shine as a result of reflected light. Moons reflect the light of their parent planet, planets reflect the light of the sun, and comets reflect the light of the sun as well. Stars, on the other hand, shine through a process called nuclear fusion, where they generate their own light and energy. Therefore, the set "moons, planets, and comets" is the only set that contains objects that shine as a result of reflected light.

When an object is placed in a fluid, it experiences an upward force known as buoyancy. This force is equal to the weight of the fluid that the object displaces. In this case, the pine wood is floating on the surface of the lake because the water exerts an upward force on it that is equal to the weight of the water that the wood displaces. This buoyant force counteracts the downward force of gravity, allowing the wood to float.

The athlete can run 9 kilometers in 1 hour, which means the athlete's average speed is 9 kilometers per hour. If the athlete runs at the same average speed for 30 minutes, which is half an hour, the athlete will cover half the distance. Therefore, the athlete will travel 9 kilometers.