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NYS Grade 8 Science study materials
NYS Grade 8 Science study resources

NYS Grade 8 Science practice questions

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Question 1Physical Sciences

Which statement describes the arrangement and motion of particles in a gas?

  1. Particles are locked in a repeating pattern and only vibrate.
  2. Particles are close together but slide past one another.
  3. Particles are far apart and move freely past one another. Correct answer.
  4. Particles are fixed in position and do not move.

Explanation

In a gas, particles have enough kinetic energy to overcome attractions and are spread far apart, moving randomly in all directions. This freedom of motion lets a gas expand and fill its container. Fixed patterns describe solids, and closely packed sliding particles describe liquids.

Question 2Physical Sciences

A ball rolls down a ramp and speeds up. Which statement best describes the energy change?

  1. Total mechanical energy increases as the ball rolls down.
  2. Kinetic energy decreases as potential energy increases.
  3. Both potential energy and kinetic energy decrease.
  4. Potential energy decreases as kinetic energy increases. Correct answer.

Explanation

As the ball moves lower, it loses gravitational potential energy because its height decreases. That energy is converted into kinetic energy, so the ball's speed increases. In an ideal system, total mechanical energy stays constant.

Question 3Physical Sciences

A metal spoon left in a cup of hot soup becomes warm. Which process transfers thermal energy through the metal?

  1. Convection
  2. Conduction Correct answer.
  3. Radiation
  4. Evaporation

Explanation

Conduction transfers thermal energy through direct contact between particles, as faster-moving particles in the hot soup collide with slower particles in the spoon. Metals conduct heat well because their free electrons carry energy quickly. Convection moves energy through fluids, and radiation travels by electromagnetic waves.

Question 4Physical Sciences

A block has a mass of 60 g and a volume of 20 cm³. What is the density of the block?

  1. 3 g/cm³ Correct answer.
  2. 1200 g/cm³
  3. 40 g/cm³
  4. 0.33 g/cm³

Explanation

Density is mass divided by volume, so divide 60 g by 20 cm³. The result is 3 g/cm³, meaning each cubic centimeter of the block has a mass of 3 g.

Question 5Physical Sciences

A runner travels 100 m in 20 s. What is the runner's average speed?

  1. 2000 m/s
  2. 0.2 m/s
  3. 5 m/s Correct answer.
  4. 20 m/s

Explanation

Average speed equals total distance divided by total time. Dividing 100 m by 20 s gives 5 m/s.

Question 6Physical Sciences

Two students push a box in the same direction with forces of 30 N and 20 N. A friction force of 10 N acts in the opposite direction. What is the net force on the box?

  1. 10 N in the direction of the pushes
  2. 50 N in the direction of the pushes
  3. 60 N in the direction of the pushes
  4. 40 N in the direction of the pushes Correct answer.

Explanation

The two pushes act in the same direction, so add them: 30 N + 20 N = 50 N. Friction acts opposite the motion, so subtract 10 N. The net force is 40 N in the direction of the pushes.

Question 7Physical Sciences

A wave has a frequency of 4 Hz and a wavelength of 2 m. What is the speed of the wave?

  1. 0.5 m/s
  2. 8 m/s Correct answer.
  3. 2 m/s
  4. 6 m/s

Explanation

Wave speed equals frequency multiplied by wavelength. Using 4 Hz × 2 m gives 8 m/s.

Question 8Physical Sciences

In a closed container, 12 g of carbon reacts completely with 32 g of oxygen to form carbon dioxide. What mass of carbon dioxide forms?

  1. 384 g
  2. 32 g
  3. 44 g Correct answer.
  4. 20 g

Explanation

The law of conservation of mass says mass is neither created nor destroyed in a closed system. The reactants have a total mass of 12 g + 32 g = 44 g, so the carbon dioxide produced must also have a mass of 44 g.

Question 9Physical Sciences

Two identical light bulbs are connected in parallel to a battery. The filament in one bulb breaks, so no current can flow through that branch. What happens to the other bulb?

  1. It remains lit because its branch is still a complete circuit. Correct answer.
  2. It flickers on and off because the circuit is now open.
  3. It becomes brighter because it receives all the current.
  4. It goes out because the battery stops supplying current.

Explanation

In a parallel circuit, each branch is connected directly across the battery, so each branch can carry current independently. Breaking one branch stops current only in that branch. The other bulb still has a complete path and stays lit.

Question 10Physical Sciences

An atom has 11 protons, 12 neutrons, and 11 electrons. Which statement correctly identifies this atom and its charge?

  1. It is a sodium atom with mass number 23 and no net charge. Correct answer.
  2. It is a sodium ion with a +1 charge and mass number 23.
  3. It is a neon atom with mass number 23 and no net charge.
  4. It is a magnesium atom with mass number 24 and a +1 charge.

Explanation

The number of protons determines the element: 11 protons is sodium. Mass number is protons plus neutrons, so 11 + 12 = 23. Because the atom has 11 electrons, equal to its protons, the positive and negative charges balance and the atom is neutral.

Question 11Physical Sciences

A student stirs a mixture of ice and liquid water in a beaker and measures the temperature. It stays at 0 °C until all the ice has melted, even though the beaker keeps gaining thermal energy. Which statement best explains why the temperature does not rise while the ice melts?

  1. The ice releases thermal energy to its surroundings as fast as it absorbs thermal energy.
  2. The added energy overcomes attractions between particles, changing ice into liquid water. Correct answer.
  3. The added energy increases the average kinetic energy of the water molecules.
  4. The particles stop moving while both ice and liquid water are present.

Explanation

During melting, the temperature stays at 0 °C because the thermal energy added is used to pull particles apart and overcome the attractions that hold the solid together. The average kinetic energy of the particles, which is what a thermometer measures, does not increase until all the ice has melted.

Question 12Physical Sciences

A rubber balloon is rubbed with a wool cloth and picks up extra electrons. Which statement correctly describes the balloon's charge and explains why it then attracts small bits of paper?

  1. The balloon becomes negatively charged, because it now has more electrons than protons. Correct answer.
  2. The balloon becomes positively charged, because electrons carry a positive charge.
  3. The balloon becomes negatively charged, because the wool cloth lost protons to the balloon.
  4. The balloon stays neutral, because rubbing only transfers thermal energy between the objects.

Explanation

Rubbing transfers electrons from the wool to the balloon, so the balloon ends up with more electrons (negative) than protons (positive) and has a net negative charge. A charged balloon attracts neutral paper bits because its charge rearranges charges within the paper, producing an attractive electric force.

Question 13Physical Sciences

A swimmer pushes backward against the water with her hands and moves forward. Which statement best explains why she moves forward?

  1. The water pushes forward on the swimmer with a force equal in size to her backward push. Correct answer.
  2. The swimmer moves forward because the weight of the water pushes her along.
  3. The water has less mass than the swimmer, so it cannot push back on her.
  4. The swimmer's forward force on herself is larger than the force she applies to the water.

Explanation

For every action force there is an equal and opposite reaction force. The swimmer pushes the water backward, so the water pushes the swimmer forward with a force of the same size, and that forward force is what moves her.

Question 14Physical Sciences

A solid cube has a density of 0.8 g/cm³. It is placed in a container of water, which has a density of 1.0 g/cm³, and released. Which statement describes what the cube does and gives the best reason for it?

  1. It sinks, because any solid object sinks when it is placed in water.
  2. It floats, because its density is less than the density of water. Correct answer.
  3. It floats, because its weight disappears once it is fully surrounded by water.
  4. It sinks, because its volume is smaller than the volume of the water in the container.

Explanation

An object floats in a fluid when its density is lower than the fluid's density. At 0.8 g/cm³ the cube is less dense than water, so the buoyant force on the partly submerged cube balances its weight and it floats.

Question 15Physical Sciences

A battery, a switch, and two light bulbs are connected in a single series loop. A student loosens one bulb until it no longer makes contact with its socket. What happens to the other bulb, and why?

  1. It becomes brighter, because the loosened bulb no longer uses any energy.
  2. It goes out, because the remaining bulb is now connected in parallel with the battery.
  3. It goes out, because the broken loop stops current everywhere in the circuit. Correct answer.
  4. It stays equally bright, because each bulb still has its own separate path.

Explanation

In a series circuit there is only one path for current, so loosening one bulb breaks that path and stops current through every part of the circuit. Both bulbs go dark, not just the loosened one.

Question 16Physical Sciences

The equation for the formation of water is 2H₂ + O₂ → 2H₂O. Which statement correctly describes what the coefficients show about the atoms in this reaction?

  1. The total number of molecules is the same before and after the reaction takes place.
  2. Two hydrogen atoms and two oxygen atoms are rearranged into two water molecules.
  3. Four hydrogen atoms and two oxygen atoms are rearranged into two water molecules. Correct answer.
  4. Two new oxygen atoms are created during the reaction that were not there before.

Explanation

The coefficients give the number of each particle: 2H₂ is four hydrogen atoms, O₂ is two oxygen atoms, and 2H₂O contains four hydrogen atoms and two oxygen atoms. The atoms are only rearranged, which is what the law of conservation of matter requires.

Question 17Physical Sciences

One guitar string vibrates 220 times per second. A second string vibrates 440 times per second with the same amplitude. How do the sounds made by the two strings compare?

  1. The second string sounds lower in pitch because it vibrates faster.
  2. The second string sounds higher in pitch and also louder.
  3. The second string sounds louder at the same pitch.
  4. The second string sounds higher in pitch at the same loudness. Correct answer.

Explanation

Pitch depends on frequency and loudness depends on amplitude. Doubling the frequency from 220 Hz to 440 Hz raises the pitch, while the unchanged amplitude keeps the loudness the same.

Question 18Physical Sciences

An electric motor does 600 J of work while lifting a crate in 3 s. What is the power output of the motor?

  1. 600 W
  2. 200 W Correct answer.
  3. 0.005 W
  4. 1,800 W

Explanation

Power is the rate at which work is done, so power equals work divided by time: 600 J ÷ 3 s = 200 W. A watt is one joule per second, meaning the motor delivers 200 J of energy every second.

Question 19Physical Sciences

Two identical carts roll along the same track. Cart A moves at 2 m/s and cart B moves at 4 m/s. How does the kinetic energy of cart B compare with the kinetic energy of cart A?

  1. Cart B has twice the kinetic energy of cart A.
  2. Cart B has four times the kinetic energy of cart A. Correct answer.
  3. Cart B has the same kinetic energy, because both carts have the same mass.
  4. Cart B has eight times the kinetic energy of cart A.

Explanation

Kinetic energy follows KE = ½mv², so it depends on the square of the speed. Doubling the speed from 2 m/s to 4 m/s multiplies the kinetic energy by 2² = 4 when the mass stays the same.

Question 20Physical Sciences

Equal masses of metal X and metal Y absorb the same amount of thermal energy. The temperature of metal X rises 10 °C, while the temperature of metal Y rises 20 °C. Which conclusion is best supported by these observations?

  1. No conclusion can be reached, because the two metals have equal masses.
  2. Both metals must have the same specific heat, since they absorbed equal amounts of energy.
  3. Metal X has the greater specific heat, because it gained less temperature from the same energy. Correct answer.
  4. Metal Y has the greater specific heat, because its temperature rose more.

Explanation

Specific heat describes how much energy one gram of a substance must absorb to raise its temperature by 1 °C. Absorbing the same energy with a smaller temperature rise means metal X stores more energy per degree, so X has the greater specific heat.

Question 21Physical Sciences

Which change is a chemical change?

  1. Iron rusting Correct answer.
  2. Ice melting
  3. Ethanol evaporating
  4. Sugar dissolving

Explanation

A chemical change produces one or more new substances with different properties. Rust is a new substance, iron oxide, formed when iron reacts with oxygen and water. Melting, dissolving, and evaporating change only the form or arrangement of existing substances, so they are physical changes.

Question 22Physical Sciences

Which sample is best classified as a pure substance?

  1. Salt water
  2. Trail mix
  3. Air
  4. Carbon dioxide Correct answer.

Explanation

A pure substance has a fixed composition and cannot be separated into different substances by physical means. Carbon dioxide is a compound made of carbon and oxygen in a fixed ratio, so it is a pure substance. Trail mix, salt water, and air each contain two or more substances mixed together.

Question 23Physical Sciences

A ringing bell is inside a clear jar. A pump removes air until the jar is nearly a vacuum. What does an observer hear?

  1. It becomes fainter because sound needs a medium. Correct answer.
  2. It stays the same because sound needs no matter.
  3. It becomes louder because less air absorbs it.
  4. It stops at once because the bell stops vibrating.

Explanation

Sound is a mechanical wave that travels by making particles of a medium vibrate. With almost no air left in the jar, there are too few particles to carry the vibrations to the observer. The bell still vibrates, but the sound becomes fainter and eventually cannot be heard.

Question 24Physical Sciences

A car's speed increases from 5 m/s to 25 m/s in 8 s. What is the car's acceleration?

  1. 3.1 m/s²
  2. 20 m/s²
  3. 2.5 m/s² Correct answer.
  4. 30 m/s²

Explanation

Acceleration is the change in velocity divided by the time interval. The change in speed is 25 m/s minus 5 m/s, which equals 20 m/s, and 20 m/s divided by 8 s is 2.5 m/s². This means the car's speed increases by 2.5 m/s every second.

Question 25Physical Sciences

A bus moving at constant speed stops suddenly. A standing passenger falls forward. Which statement best explains this?

  1. The passenger's mass decreases when the bus stops.
  2. A backward force from the seats pushes the passenger forward.
  3. Gravity pulls the passenger toward the front of the bus.
  4. The passenger keeps moving forward because of inertia. Correct answer.

Explanation

According to Newton's first law, an object in motion stays in motion unless a net force acts on it. When the bus stops, the passenger's body continues moving forward at the bus's original speed until a force, such as friction or a handrail, slows it. The passenger is not pushed forward by a new force; inertia explains the motion.

Question 26Physical Sciences

How many atoms are present in one formula unit of Ca(NO₃)₂?

  1. 7
  2. 11
  3. 5
  4. 9 Correct answer.

Explanation

The formula shows one calcium atom, and the subscript 2 outside the parentheses applies to everything inside. That gives two nitrogen atoms and six oxygen atoms, because each nitrate group has three oxygen atoms. Adding 1 + 2 + 6 gives a total of 9 atoms.

Question 27Physical Sciences

A pot of water is heated from the bottom. Water near the bottom warms, rises, and cooler water moves down to replace it. Which process transfers thermal energy through the water in this way?

  1. Convection Correct answer.
  2. Reflection
  3. Radiation
  4. Conduction

Explanation

Convection transfers thermal energy by the movement of a fluid, such as a liquid or gas. Warm water is less dense, so it rises while cooler, denser water sinks, creating circulating currents. Conduction would require direct contact between particles without the bulk movement of the water.

Question 28Physical Sciences

A student wraps wire around an iron nail and connects the wire to a battery to make an electromagnet. Which change will make the electromagnet stronger?

  1. Removing the battery from the circuit
  2. Replacing the iron nail with a plastic rod
  3. Increasing the number of turns of wire Correct answer.
  4. Spreading the coils farther apart along the nail

Explanation

The strength of an electromagnet increases with more current and more turns of wire in the coil. Adding turns creates a stronger magnetic field around the iron core. The iron core also matters because it becomes magnetized and strengthens the field.

Question 29Physical Sciences

A 12 V battery causes a current of 2 A to flow through a small heater for 5 s. How much electrical energy does the heater transfer?

  1. 120 J Correct answer.
  2. 60 J
  3. 24 J
  4. 240 J

Explanation

Electrical energy transferred equals voltage multiplied by current multiplied by time. Multiplying 12 V by 2 A gives 24 W of power, and multiplying that power by 5 s gives 120 J. The joule is the unit of energy, so the answer is 120 J.

Question 30Physical Sciences

A sealed syringe contains air at room temperature. A student pushes the plunger in, reducing the volume of the trapped air while the temperature stays the same. What happens to the pressure of the air, and why?

  1. It increases because particles hit the walls more often. Correct answer.
  2. It decreases because the particles have more space to move.
  3. It increases because each particle expands in size.
  4. It stays the same because the number of particles is unchanged.

Explanation

Pressure is caused by gas particles colliding with the walls of their container. When the same number of particles is squeezed into a smaller volume, the particles hit the walls more frequently, so the pressure increases. The particles themselves do not change size, and the temperature remains constant.

Question 31Physical Sciences

An atom of chlorine has an atomic number of 17 and a mass number of 35. How many neutrons are in the nucleus of this atom?

  1. 18 Correct answer.
  2. 52
  3. 17
  4. 35

Explanation

The atomic number gives the number of protons, which is 17. The mass number is the total of protons and neutrons, so the neutron count is 35 − 17 = 18.

Question 32Physical Sciences

A copper wire connects a battery to a light bulb, and the wire is covered with a layer of plastic. Why is the plastic covering useful?

  1. Plastic is magnetic, so it pulls the current along the wire.
  2. Plastic is a good conductor, so it helps current flow along the wire.
  3. Plastic raises the battery voltage so the bulb glows more brightly.
  4. Plastic is an insulator, so it keeps current inside the wire. Correct answer.

Explanation

Plastic is an insulator, so its electrons are not free to move and carry current. The coating keeps the current inside the copper wire and protects a person who touches the wire from a shock.

Question 33Physical Sciences

Which pH value indicates a strongly acidic solution?

  1. pH 9
  2. pH 13
  3. pH 7
  4. pH 2 Correct answer.

Explanation

A solution with pH 2 is strongly acidic because it has a high concentration of hydrogen ions. Values below 7 are acidic, 7 is neutral, and values above 7 are basic.

Question 34Physical Sciences

A beaker holds a mixture of sand and salt water. Which procedure will separate the dissolved salt from the water?

  1. Use a magnet to pull the dissolved salt out of the solution.
  2. Pour the mixture through filter paper, which traps the dissolved salt.
  3. Heat the mixture until the water boils off, then condense the vapor in another container. Correct answer.
  4. Let the mixture stand until the sand dissolves in the water.

Explanation

Dissolved salt passes through filter paper, so filtering separates only undissolved sand. Boiling the water away and condensing the vapor leaves the salt behind and recovers the water, a process called distillation.

Question 35Physical Sciences

A sound wave traveling through air has a frequency of 170 Hz and a speed of 340 m/s. What is its wavelength?

  1. 0.5 m
  2. 2 m Correct answer.
  3. 170 m
  4. 57,800 m

Explanation

The wave equation is speed = frequency × wavelength, so wavelength = speed ÷ frequency. Substituting the values gives 340 m/s ÷ 170 Hz = 2 m.

Question 36Physical Sciences

In a closed container, 4 g of hydrogen reacts completely with 32 g of oxygen to form water. What mass of water forms?

  1. 28 g
  2. 32 g
  3. 36 g Correct answer.
  4. 128 g

Explanation

The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The mass of the products equals the total mass of the reactants, so 4 g + 32 g = 36 g.

Question 37Physical Sciences

A lever is used to lift a heavy rock. The effort arm is 2.0 m long and the resistance arm is 0.50 m long. Ignoring friction, what is the ideal mechanical advantage of this lever?

  1. 1.5
  2. 4.0 Correct answer.
  3. 2.0
  4. 0.25

Explanation

The ideal mechanical advantage of a lever equals the effort arm length divided by the resistance arm length. Here 2.0 m ÷ 0.50 m = 4.0, so the lever multiplies the applied force by 4.

Question 38Physical Sciences

A straw standing in a glass of water appears broken at the water's surface. Which statement best explains this observation?

  1. Light changes speed and bends as it passes from water into air. Correct answer.
  2. Water produces its own light, which overlaps the image of the straw.
  3. Light travels through water and air at exactly the same speed.
  4. Light is absorbed by the water and does not reach the observer's eye.

Explanation

Light travels at different speeds in water and in air, so its path bends when it crosses the boundary between them. This bending, called refraction, makes the straw appear broken at the surface.

Question 39Physical Sciences

A 9.0 V battery is connected to two resistors in series: a 3.0 Ω resistor and a 6.0 Ω resistor. What is the voltage across the 3.0 Ω resistor?

  1. 1.0 V
  2. 4.5 V
  3. 3.0 V Correct answer.
  4. 6.0 V

Explanation

Resistors in series add to a total resistance of 3.0 Ω + 6.0 Ω = 9.0 Ω, so the current is 9.0 V ÷ 9.0 Ω = 1.0 A. The voltage across the 3.0 Ω resistor is then 1.0 A × 3.0 Ω = 3.0 V.

Question 40Physical Sciences

A cyclist rides 300 m at a speed of 6 m/s and then rides another 200 m at 4 m/s. What is the cyclist's average speed for the entire trip?

  1. 5.0 m/s Correct answer.
  2. 4.8 m/s
  3. 5.2 m/s
  4. 6.0 m/s

Explanation

Average speed is total distance divided by total time, not the average of the two speeds. The times are 300 m ÷ 6 m/s = 50 s and 200 m ÷ 4 m/s = 50 s, so the average speed is 500 m ÷ 100 s = 5.0 m/s.

Question 41Physical Sciences

A ball is held at the top of a ramp and then released. As it rolls down the ramp, ignoring friction, which energy transformation is occurring?

  1. Chemical energy changes into electrical energy.
  2. Gravitational potential energy changes into kinetic energy. Correct answer.
  3. Kinetic energy changes into gravitational potential energy.
  4. Thermal energy changes into sound energy.

Explanation

At the top, the ball has gravitational potential energy because of its height. As it moves lower and speeds up, that stored energy becomes kinetic energy; ignoring friction, the total mechanical energy stays about the same.

Question 42Physical Sciences

A student rubs two identical balloons with wool. Both balloons become negatively charged and then push away from each other. Which statement best explains the repulsion?

  1. One balloon gained protons, and the other lost protons.
  2. The wool transferred north magnetic poles to both balloons.
  3. The balloons repel because their masses are equal.
  4. Both balloons have the same type of charge, so they repel. Correct answer.

Explanation

Rubbing transfers electrons between the wool and the balloons. Both balloons end up with extra electrons, giving them like negative charges, and like charges repel.

Question 43Physical Sciences

A bar magnet is broken into two separate pieces. Which statement describes the magnetic poles of the two pieces?

  1. Only the larger piece keeps a north pole and a south pole.
  2. Each piece has both a north pole and a south pole. Correct answer.
  3. Both pieces become unmagnetized because the magnet was broken.
  4. One piece has only a north pole, and the other has only a south pole.

Explanation

Magnetic poles always occur in pairs. Breaking a magnet produces smaller magnets, and each new piece has its own north pole and south pole.

Question 44Physical Sciences

A student finds a solid sample with a mass of 54 g and a volume of 18 cm³. The sample is placed in water, which has a density of 1.0 g/cm³. What is the density of the sample, and will it sink in water?

  1. 0.33 g/cm³; it will float.
  2. 0.33 g/cm³; it will sink.
  3. 3.0 g/cm³; it will float.
  4. 3.0 g/cm³; it will sink. Correct answer.

Explanation

Density equals mass divided by volume, so 54 g ÷ 18 cm³ = 3.0 g/cm³. A sample with a density greater than water's density of 1.0 g/cm³ will sink.

Question 45Physical Sciences

A beaker of water is heated at a steady rate and begins to boil. While the water is boiling, its temperature stays at 100°C even though thermal energy continues to enter. Why does the temperature stay the same?

  1. The thermometer cannot measure temperatures above 100°C.
  2. The added energy is stored as extra mass inside each of the water particles.
  3. The water stops absorbing thermal energy once it reaches 100°C.
  4. The energy is used to separate water particles as the liquid changes to gas. Correct answer.

Explanation

During a phase change, added thermal energy goes into separating particles rather than increasing their average kinetic energy. Since temperature measures average kinetic energy, the temperature remains constant while boiling continues.

Question 46Physical Sciences

A box is pushed to the right with a force of 20 N. Friction acts to the left with a force of 12 N. What is the net force on the box, and how does the box move?

  1. 8 N to the left; the box accelerates left.
  2. 8 N to the right; the box accelerates right. Correct answer.
  3. 32 N to the right; the box accelerates right.
  4. 12 N to the left; the box moves at constant speed.

Explanation

The forces point in opposite directions, so subtract the smaller force from the larger one: 20 N − 12 N = 8 N to the right. An unbalanced net force causes acceleration in the direction of the net force.

Question 47Physical Sciences

Two identical light bulbs are connected in parallel to a battery. One bulb burns out and stops conducting. What happens to the other bulb?

  1. It goes out because the circuit is now open.
  2. It becomes brighter because it receives all the current.
  3. It flickers on and off because the current reverses direction.
  4. It stays lit because its branch still connects to the battery. Correct answer.

Explanation

In a parallel circuit, each branch provides a separate path for current. If one branch is broken, current can still flow through the other branch, so the working bulb stays lit.

Question 48Physical Sciences

A student lifts a 50 N box straight up a distance of 2.0 m in 4.0 s. How much power does the student use to lift the box?

  1. 100 W
  2. 12.5 W
  3. 200 W
  4. 25 W Correct answer.

Explanation

Work equals force times distance: 50 N × 2.0 m = 100 J. Power equals work divided by time: 100 J ÷ 4.0 s = 25 W.

Question 49Physical Sciences

A light ray strikes a flat mirror. The angle between the incoming ray and the normal is 35°. What is the angle between the incoming ray and the reflected ray?

  1. 55°
  2. 110°
  3. 35°
  4. 70° Correct answer.

Explanation

The law of reflection says the angle of incidence equals the angle of reflection, both measured from the normal. The incoming and reflected rays are on opposite sides of the normal, so the angle between them is 35° + 35° = 70°.

Question 50Physical Sciences

At 20°C, 50 g of water can dissolve at most 18 g of a certain solid. A student stirs 25 g of the solid into 50 g of water at 20°C and waits. Which statement describes the resulting mixture?

  1. 18 g dissolves; 7 g remains undissolved in a saturated solution. Correct answer.
  2. All 25 g dissolves, and the solution is saturated at 20°C.
  3. All 25 g dissolves, creating an unsaturated solution at 20°C.
  4. No solid dissolves at all because the water is already saturated before stirring.

Explanation

Solubility gives the maximum mass that can dissolve in a given amount of water at a set temperature. Here the maximum is 18 g, so 7 g of the 25 g remains undissolved and the solution is saturated.