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Praxis Physical Science 5485 practice questions

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Question 1Nature of Science and Engineering

In physical science, which description best characterizes a hypothesis?

  1. an untestable personal belief about how nature works
  2. a statement that summarizes a consistent natural pattern
  3. a testable prediction about a relationship between variables Correct answer.
  4. a well-supported explanation that unifies many observations

Explanation

A hypothesis is a tentative, testable statement that predicts an outcome and can be supported or refuted by evidence. Broad explanatory frameworks are theories, while compact descriptions of regularities are laws. Personal beliefs that cannot be tested fall outside scientific inquiry.

Question 2Nature of Science and Engineering

Which pairing of an SI base unit with the quantity it measures is correct?

  1. kelvin - amount of substance
  2. mole - thermodynamic temperature
  3. ampere - electric current Correct answer.
  4. candela - pressure

Explanation

The ampere is the SI base unit of electric current. The kelvin measures thermodynamic temperature, the mole measures amount of substance, and the candela measures luminous intensity; pressure is a derived quantity, not a base one.

Question 3Nature of Science and Engineering

A student tests whether a new insulation reduces heat loss by comparing a container wrapped in the new material with an identical container wrapped in the original insulation. The second container primarily serves as...

  1. a calibration standard for the thermometer
  2. a replicate that increases the sample size
  3. a treatment that changes the independent variable
  4. a control for baseline comparison Correct answer.

Explanation

A control is treated the same as the experimental group except for the variable being tested, so it establishes the baseline needed to attribute any difference to the new insulation. Replicates would be additional containers within the same treatment, not a different treatment.

Question 4Nature of Science and Engineering

A team varies the concentration of a catalyst and measures how long a reaction takes to reach completion while holding temperature and pressure constant. In this investigation, the independent variable is...

  1. the pressure maintained during the reaction
  2. the time required for the reaction to finish
  3. the concentration of the catalyst Correct answer.
  4. the temperature of the reaction mixture

Explanation

The independent variable is the factor deliberately changed by the investigator, which here is catalyst concentration. Reaction time is the dependent variable because it is measured as a response, and temperature and pressure are controlled variables held constant.

Question 5Nature of Science and Engineering

The accepted density of a metal is 8.9 g/cm³. Which set of repeated measurements is precise but not accurate?

  1. 8.9, 7.2, 9.8, 8.1 g/cm³
  2. 7.0, 8.2, 9.4, 10.1 g/cm³
  3. 7.1, 7.2, 7.1, 7.2 g/cm³ Correct answer.
  4. 8.9, 8.8, 9.0, 8.9 g/cm³

Explanation

Precision refers to how closely repeated measurements agree with one another, while accuracy refers to how close they are to the accepted value. The set 7.1, 7.2, 7.1, 7.2 is tightly clustered but centered well below 8.9 g/cm³, so it is precise but inaccurate.

Question 6Nature of Science and Engineering

A sample has a mass of 12.34 g and a volume of 3.2 mL. Applying significant-figure rules to the division, the density should be reported as...

  1. 3.9 g/mL Correct answer.
  2. 3.86 g/mL
  3. 4 g/mL
  4. 3.856 g/mL

Explanation

When dividing measured quantities, the result may keep only as many significant figures as the measurement with the fewest, which is the volume with two. The calculated value 3.856... g/mL rounds to two significant figures, giving 3.9 g/mL.

Question 7Nature of Science and Engineering

The primary function of peer review in scientific publication is to...

  1. confirm that the results can be reproduced in the reviewers' laboratories
  2. revise the reported results so they agree with the current consensus
  3. ensure that the findings will later be accepted as a scientific law
  4. judge whether methods, analysis, and conclusions meet standards Correct answer.

Explanation

Peer review is a quality-control process in which independent experts evaluate the design, evidence, reasoning, and significance of a manuscript before publication. It does not replicate the work or guarantee acceptance of the findings, and reviewers do not alter data to fit consensus.

Question 8Nature of Science and Engineering

A design team must keep a prototype backpack under 1.2 kg and under $40 in materials while still carrying a 15 kg load. In engineering design, these requirements are best classified as...

  1. sources of random error that affect prototype measurements
  2. dependent variables that are measured during field trials
  3. hypotheses that must be tested in a controlled experiment
  4. criteria and constraints defining acceptable solutions Correct answer.

Explanation

Engineering design specifies criteria, which are goals the solution should meet, and constraints, which are limits on cost, mass, safety, time, or materials. Together they define which solutions are acceptable before prototypes are built and tested.

Question 9Nature of Science and Engineering

Which statement best describes the relationship between scientific theories and scientific laws?

  1. Theories become laws after enough measurements have been collected.
  2. Theories explain phenomena; laws describe consistent patterns. Correct answer.
  3. Theories concern unobservable entities, whereas laws concern only observables.
  4. Laws are theories that have been proven beyond any possibility of revision.

Explanation

A scientific theory is an evidence-supported explanatory framework for why phenomena occur, while a scientific law is a concise statement of a consistent relationship or pattern. They serve different roles and neither is a stepping stone to the other; both remain open to revision.

Question 10Nature of Science and Engineering

A study finds that students using a computer simulation score higher on a physics test than students using a textbook, but the simulation group also received 50% more instruction time. The strongest threat to the study's conclusion is that...

  1. the test may not have measured the intended content
  2. the sample size may have been too small to detect a real effect
  3. the textbook group may have had less initial interest in physics
  4. instruction time confounds the comparison between groups Correct answer.

Explanation

A confounding variable is an additional factor that differs between comparison groups and could produce the observed effect. Because instruction time varied along with the type of resource, the score difference cannot be attributed confidently to the simulation alone.

Question 11Nature of Science and Engineering

In the engineering design process, what is the main purpose of constructing a prototype?

  1. To document the team's budget for investors
  2. To test the design against requirements Correct answer.
  3. To serve as the final product for consumers
  4. To eliminate the need for further testing

Explanation

A prototype is a testable version of a design built to reveal whether the design meets its stated criteria and constraints. Results from prototype testing guide iterative revisions before final production. It is not a finished consumer product and does not remove the need for testing.

Question 12Nature of Science and Engineering

Why do physical scientists often use models to study systems such as atoms or galaxies?

  1. Models prove that a scientific theory is permanently correct
  2. Models eliminate all uncertainty from scientific measurements
  3. Models replace the need for collecting experimental evidence
  4. Models represent systems too small or too large to observe Correct answer.

Explanation

Models are representations used when a system is too small, too large, too distant, or too complex for direct study. They help scientists visualize, predict, and test ideas, but they remain approximations supported by evidence. Models do not replace experiments or remove uncertainty.

Question 13Nature of Science and Engineering

A student tests whether a new insulating wrap keeps a beverage colder than plain foil. The container wrapped in plain foil is best described as which part of the investigation?

  1. The control group Correct answer.
  2. The dependent variable
  3. The independent variable
  4. The experimental group

Explanation

The control group provides a baseline for comparison because it does not receive the new treatment. Any difference between the control and experimental groups can then be attributed more confidently to the insulating wrap. The independent variable is the type of wrap, and the dependent variable is the temperature change.

Question 14Nature of Science and Engineering

A digital balance used in a lab consistently reads 0.40 g higher than the true mass for every sample. Which description best fits this measurement problem?

  1. A systematic error that shifts every reading the same way Correct answer.
  2. A calculation error caused by using the wrong formula
  3. Random error that can be reduced by averaging many trials
  4. A precision problem that makes repeated readings vary widely

Explanation

A systematic error is a consistent bias, such as a miscalibrated balance that reads high by the same amount each time. It reduces accuracy but may still allow precise, repeatable readings. Averaging repeated trials cannot remove a constant offset; the instrument must be recalibrated.

Question 15Nature of Science and Engineering

A researcher finds that towns with higher ice-cream sales also have higher rates of drowning deaths. Which conclusion is most defensible?

  1. Drowning deaths cause ice-cream sales to increase
  2. Correlation exists, but a third factor may explain both Correct answer.
  3. The relationship proves that ice cream is unsafe near water
  4. Eating ice cream causes a person to drown

Explanation

A correlation between two variables does not by itself establish that one causes the other. A confounding variable, such as warm weather, could increase both ice-cream sales and water recreation, raising drowning risk. Controlled studies and plausible mechanisms are needed before causal claims are made.

Question 16Nature of Science and Engineering

A student investigates how water temperature affects the time needed for a sugar cube to dissolve. Which procedure best isolates the independent variable?

  1. Vary temperature and stirring speed together to save time
  2. Keep sugar amount, stirring, and cube size constant; vary temperature Correct answer.
  3. Use hot water in every trial and change the sugar cube size
  4. Use different amounts of sugar in each trial and change the water temperature

Explanation

The independent variable is water temperature, so all other factors that could affect dissolving time must be held constant. Sugar amount, stirring, and cube size should be controlled while only temperature changes. Varying multiple factors at once makes it impossible to attribute differences to temperature alone.

Question 17Nature of Science and Engineering

A team claims that a lake is becoming more acidic over time. Which evidence would most strongly support this claim?

  1. The lake is located near a factory that uses acids
  2. A multi-year record shows average pH decreasing steadily Correct answer.
  3. A fisherman reports that the water looks more acidic than before
  4. One water sample taken today has a pH of 6.0

Explanation

A sustained decline in average pH over many years is direct, quantitative evidence that the lake is becoming more acidic. A single measurement lacks a baseline, personal impressions are anecdotal, and the presence of a factory does not by itself show an effect. Scientific claims are strongest when supported by repeated measurements showing a consistent trend.

Question 18Nature of Science and Engineering

A student heats a sample and plots temperature on the vertical axis against time on the horizontal axis. The graph is a straight line with a positive slope. What does the slope represent?

  1. The total heat added to the sample
  2. The rate at which temperature changes Correct answer.
  3. The mass of the sample being heated
  4. The final temperature reached by the sample

Explanation

The slope of a linear graph equals the change in the vertical quantity divided by the change in the horizontal quantity. Here, slope equals the change in temperature divided by the change in time, which is the rate of temperature change. It does not give total heat unless the sample's mass and specific heat are also known.

Question 19Nature of Science and Engineering

A design team compares two prototypes of a portable water filter. Prototype A meets the flow-rate requirement but exceeds the maximum cost. Prototype B meets the cost limit but filters too slowly. What is the most appropriate next step in the design process?

  1. Select Prototype B because staying within budget is the only constraint
  2. Revise the design to fix the failing constraint and retest Correct answer.
  3. Abandon the project because no prototype meets every requirement
  4. Select Prototype A because performance always outweighs cost

Explanation

Engineering design requires satisfying all criteria and constraints, not sacrificing one permanently for another. When prototypes fail a constraint, the team should revise the design and retest it iteratively. Neither prototype is ready for selection, and abandoning the project is premature.

Question 20Nature of Science and Engineering

A single laboratory reports that a new material superconducts at a surprisingly high temperature. Why should the scientific community withhold acceptance until the result is replicated?

  1. Because scientific claims are decided by majority vote of the public
  2. Because a single result may reflect error or an uncontrolled variable Correct answer.
  3. Because new materials are rarely interesting to scientists
  4. Because replication guarantees that the original hypothesis was correct

Explanation

Scientific claims require converging evidence, and a single result may arise from random error, instrument problems, or an uncontrolled variable. Replication by independent investigators tests whether the finding is reliable and generalizable. Replication does not guarantee correctness, but it is a necessary check before broad acceptance.

Question 21Nature of Science and Engineering

A student investigating how the temperature of a metal wire affects its resistance states, "Resistance will be recorded as the voltage across the wire divided by the current through the wire." This statement is best described as

  1. an operational definition of resistance Correct answer.
  2. a testable hypothesis about the wire's behavior
  3. a scientific law relating voltage and current
  4. a theoretical model of electron flow

Explanation

An operational definition specifies exactly how a quantity will be measured or calculated so that other investigators can repeat the procedure. It does not predict an outcome, explain a mechanism, or state a broad regularity observed in nature. Here it fixes the procedure for obtaining resistance rather than advancing a claim to be tested.

Question 22Nature of Science and Engineering

A student drops a steel ball from a fixed height ten times and records the fall time for each trial. The times scatter by about 0.05 s around the mean. Which action would best increase confidence in the reported mean fall time?

  1. Round each measured time to the nearest whole second
  2. Report the single trial closest to the expected value
  3. Collect additional trials and average all the times Correct answer.
  4. Increase the drop height and repeat the ten trials

Explanation

Random scatter among repeated measurements is best reduced by averaging more independent trials, which makes the reported mean more reliable. Choosing a favored trial introduces bias, rounding discards information, and changing the drop height alters the experimental condition instead of improving the estimate.

Question 23Nature of Science and Engineering

A company tests a new polymer by cutting all tensile specimens from one small region of a single molded sheet; the results are highly consistent. Why is this evidence weak for predicting performance of the full production run?

  1. The specimens may not represent other regions or batches. Correct answer.
  2. The test measured tensile strength rather than stiffness.
  3. Consistent results from one test cannot support any scientific claim at all.
  4. A single molded sheet cannot be tested for tensile strength.

Explanation

Measurements from one localized region show only that the material is consistent there; properties of a molded polymer can vary across a sheet and between production batches. Representativeness requires sampling across the regions or batches about which the company intends to make a claim.

Question 24Nature of Science and Engineering

A computer model of heat flow through a wall matches field measurements closely at 20°C but predicts temperatures several degrees higher than measured when the wall is tested at 40°C. What is the most appropriate interpretation?

  1. Its assumptions may fail at higher temperatures, so it needs revision. Correct answer.
  2. The model should be discarded entirely because a single mismatch proves it false.
  3. The model is already validated because it matched the field data at 20°C.
  4. The field measurements at 40°C must be incorrect because models are based on theory.

Explanation

A model's assumptions are often valid only within a limited range, so agreement at 20°C does not guarantee agreement at 40°C. A mismatch under new conditions is a signal to examine and revise assumptions and to collect further data, not to reject the model outright or to dismiss the measurements.

Question 25Physics

A runner jogs 150 m east in 10 s and then turns and jogs 150 m west in 15 s. What is the magnitude of the runner's average velocity for the entire trip?

  1. 12 m/s
  2. 0 m/s Correct answer.
  3. 24 m/s
  4. 6.0 m/s

Explanation

Average velocity is total displacement divided by total time. The runner returns to the starting point, so the net displacement is zero and the average velocity magnitude is zero. The nonzero average speed is found from total distance divided by total time, which is a different quantity.

Question 26Physics

A 12 V ideal battery is connected across a single 4 Ω resistor. What current flows through the resistor?

  1. 3 A Correct answer.
  2. 0.33 A
  3. 48 A
  4. 16 A

Explanation

Ohm's law states that current equals voltage divided by resistance, I = V/R. Substituting gives I = 12 V / 4 Ω = 3 A. The result is a direct application of the relationship among current, voltage, and resistance.

Question 27Physics

A sound wave has a frequency of 500 Hz and travels through air at 340 m/s. What is its wavelength?

  1. 0.0015 m
  2. 1.5 m
  3. 170,000 m
  4. 0.68 m Correct answer.

Explanation

For a wave, speed equals frequency times wavelength, so wavelength equals speed divided by frequency. Using λ = v/f gives 340 m/s ÷ 500 Hz = 0.68 m. Frequency and wavelength are inversely related when wave speed is constant.

Question 28Physics

A 10 kg crate is pushed across a horizontal floor by a 50 N horizontal force. The coefficient of kinetic friction between the crate and the floor is 0.20. What is the crate's acceleration? Use g = 9.8 m/s².

  1. 2.0 m/s²
  2. 5.0 m/s²
  3. 0.50 m/s²
  4. 3.0 m/s² Correct answer.

Explanation

The kinetic friction force is f = μmg = 0.20 × 10 kg × 9.8 m/s² = 19.6 N. The net horizontal force is 50 N − 19.6 N = 30.4 N, so a = F_net/m = 30.4 N / 10 kg ≈ 3.0 m/s². Friction must be subtracted before applying Newton's second law.

Question 29Physics

A 2.0 kg cart moving east at 3.0 m/s collides with a stationary 4.0 kg cart. The carts stick together. What is the velocity of the combined carts immediately after the collision?

  1. 1.0 m/s east Correct answer.
  2. 3.0 m/s east
  3. 1.5 m/s east
  4. 0.50 m/s east

Explanation

In a perfectly inelastic collision, momentum is conserved and the final mass is the sum of the cart masses. The initial momentum is 2.0 kg × 3.0 m/s = 6.0 kg·m/s east, and dividing by 6.0 kg total mass gives 1.0 m/s east. The carts move together after sticking.

Question 30Physics

A ray of light in air strikes a flat glass surface at an angle of incidence of 30.0°. The index of refraction of the glass is 1.50. What is the angle of refraction?

  1. 30.0°
  2. 13.2°
  3. 48.6°
  4. 19.5° Correct answer.

Explanation

Snell's law is n₁ sin θ₁ = n₂ sin θ₂. Using air as n₁ = 1.00 gives sin θ₂ = (1.00/1.50) sin 30.0° = 0.333, so θ₂ ≈ 19.5°. Light entering a denser medium bends toward the normal.

Question 31Physics

A 12 V source is connected across a parallel combination of a 6 Ω resistor and a 3 Ω resistor. What is the total current drawn from the source?

  1. 4 A
  2. 6 A Correct answer.
  3. 2 A
  4. 18 A

Explanation

For parallel resistors, 1/R_eq = 1/6 + 1/3 = 1/2, so R_eq = 2 Ω. The total current is I = V/R_eq = 12 V / 2 Ω = 6 A. The branch currents are 2 A and 4 A, which add to 6 A.

Question 32Physics

How much heat is required to raise the temperature of 0.50 kg of water from 20°C to 60°C? The specific heat capacity of water is 4,186 J/(kg·°C).

  1. 170 kJ
  2. 2.1 kJ
  3. 84 kJ Correct answer.
  4. 42 kJ

Explanation

The heat required is Q = mcΔT. Here ΔT = 60°C − 20°C = 40°C, so Q = 0.50 kg × 4,186 J/(kg·°C) × 40°C ≈ 83,720 J, or about 84 kJ. The mass, specific heat, and temperature change must all be multiplied.

Question 33Physics

A proton moves east at 2.0 × 10^5 m/s through a uniform 0.50 T magnetic field directed north. What are the magnitude and direction of the magnetic force on the proton? Use q = 1.6 × 10^-19 C.

  1. 1.6 × 10^-14 N, downward
  2. 1.6 × 10^-14 N, upward Correct answer.
  3. 3.2 × 10^-14 N, upward
  4. 0 N

Explanation

The magnetic force magnitude is F = qvB sin θ. Because east and north are perpendicular, sin θ = 1, so F = (1.6 × 10^-19 C)(2.0 × 10^5 m/s)(0.50 T) = 1.6 × 10^-14 N. By the right-hand rule, v east crossed with B north gives an upward force on a positive charge.

Question 34Physics

Light with a wavelength of 500 nm strikes a metal surface with a work function of 2.0 eV. What is the maximum kinetic energy of the emitted photoelectrons? Use hc = 1240 eV·nm.

  1. 0.48 eV Correct answer.
  2. 0 eV
  3. 4.5 eV
  4. 2.5 eV

Explanation

The photon energy is E = hc/λ = 1240 eV·nm / 500 nm = 2.48 eV. The photoelectric equation gives K_max = E_photon − φ = 2.48 eV − 2.0 eV ≈ 0.48 eV. The work function is the minimum energy needed to remove an electron.

Question 35Physics

In kinematics, which quantity is classified as a vector?

  1. Speed
  2. Displacement Correct answer.
  3. Time
  4. Mass

Explanation

A vector has both magnitude and direction. Displacement specifies a change in position in a particular direction, whereas speed, mass, and time are scalars that have magnitude only.

Question 36Physics

A book rests on a table. Earth exerts a downward gravitational force on the book. Which force is the Newton's third-law partner to this force?

  1. The normal force the book exerts downward on the table
  2. The gravitational force the table exerts on the book
  3. The normal force the table exerts upward on the book
  4. The gravitational force the book exerts upward on Earth Correct answer.

Explanation

Newton's third-law partner must be the same type of force, equal in magnitude, opposite in direction, and exerted on the other object. The partner to Earth pulling the book downward is the book pulling Earth upward gravitationally.

Question 37Physics

A motor does 600 J of work in 20 s. What is its average power output?

  1. 12 W
  2. 12,000 W
  3. 30 W Correct answer.
  4. 120 W

Explanation

Average power equals work divided by the time interval, so P = W/t = 600 J / 20 s = 30 W. Power measures the rate at which energy is transferred or work is done.

Question 38Physics

A ball is launched horizontally from the top of a 20 m high cliff with an initial speed of 8.0 m/s. Air resistance is negligible. How long does the ball take to reach the ground? Use g = 9.8 m/s².

  1. 1.6 s
  2. 1.4 s
  3. 1.8 s
  4. 2.0 s Correct answer.

Explanation

The horizontal velocity does not affect the vertical fall time. Using y = ½gt² gives t = √(2y/g) = √(2 × 20 m / 9.8 m/s²) ≈ 2.0 s.

Question 39Physics

A string 1.5 m long is fixed at both ends. The wave speed on the string is 90 m/s. What is the fundamental frequency?

  1. 60 Hz
  2. 30 Hz Correct answer.
  3. 90 Hz
  4. 45 Hz

Explanation

For a string fixed at both ends, the fundamental wavelength is twice the string length: λ = 2L = 3.0 m. The fundamental frequency is f = v/λ = 90 m/s / 3.0 m = 30 Hz.

Question 40Physics

A fixed amount of ideal gas is held at constant temperature. If its volume is reduced to one-third of its original value, what happens to its pressure?

  1. It increases by a factor of nine.
  2. It triples. Correct answer.
  3. It decreases to one-third.
  4. It remains unchanged.

Explanation

At constant temperature, Boyle's law states that pressure is inversely proportional to volume for a fixed amount of ideal gas. Reducing the volume to one-third therefore causes the pressure to become three times its original value.

Question 41Physics

Two small point charges experience an electrostatic force of magnitude 8.0 N. If the distance between them is doubled while the charges remain unchanged, what is the new force magnitude?

  1. 16 N
  2. 32 N
  3. 4.0 N
  4. 2.0 N Correct answer.

Explanation

Coulomb's law states that electrostatic force is inversely proportional to the square of the separation distance. Doubling the distance multiplies the force by 1/2² = 1/4, so the new force is 8.0 N / 4 = 2.0 N.

Question 42Physics

A spring with a spring constant of 200 N/m is compressed 0.10 m from its equilibrium length. How much elastic potential energy is stored in the spring?

  1. 20 J
  2. 2.0 J
  3. 0.10 J
  4. 1.0 J Correct answer.

Explanation

Elastic potential energy for an ideal spring is PE = ½kx². Substituting k = 200 N/m and x = 0.10 m gives PE = ½ × 200 × (0.10)² = 1.0 J.

Question 43Physics

A solid uniform disk of mass 4.0 kg and radius 0.25 m rotates about an axis through its center. A net torque of 0.50 N·m acts on the disk. What is the angular acceleration of the disk?

  1. 2.0 rad/s²
  2. 0.50 rad/s²
  3. 4.0 rad/s² Correct answer.
  4. 8.0 rad/s²

Explanation

The moment of inertia of a solid disk about its central axis is I = ½MR² = ½(4.0 kg)(0.25 m)² = 0.125 kg·m². Newton's second law for rotation gives α = τ/I = 0.50 N·m / 0.125 kg·m² = 4.0 rad/s².

Question 44Physics

The energy levels of a hydrogen atom are given by E_n = −13.6 eV / n². What is the energy of the photon emitted when an electron transitions from n = 3 to n = 2?

  1. 0.75 eV
  2. 1.89 eV Correct answer.
  3. 13.6 eV
  4. 3.40 eV

Explanation

The photon energy equals the difference between the initial and final energy levels: E_photon = E_3 − E_2. Using E_3 = −13.6/9 ≈ −1.51 eV and E_2 = −13.6/4 = −3.40 eV gives about 1.89 eV.

Question 45Physics

A stone is released from rest from a height of 20 m above the ground. Ignoring air resistance and using g = 9.8 m/s², how long does the stone take to reach the ground?

  1. 2.0 s Correct answer.
  2. 4.1 s
  3. 9.8 s
  4. 1.0 s

Explanation

For an object released from rest, the distance fallen is d = ½gt². Solving for time gives t = √(2d/g) = √(2 × 20 m / 9.8 m/s²) ≈ 2.0 s.

Question 46Physics

Two tuning forks with frequencies of 440 Hz and 444 Hz are sounded together. What beat frequency is heard?

  1. 440 Hz
  2. 4 Hz Correct answer.
  3. 2 Hz
  4. 884 Hz

Explanation

The beat frequency is the absolute difference between the two sounded frequencies. Here |444 Hz − 440 Hz| = 4 Hz.

Question 47Physics

A 10 μF capacitor is connected across a 12 V battery. What charge is stored on the capacitor?

  1. 1.2 μC
  2. 0.83 μC
  3. 120 μC Correct answer.
  4. 12 μC

Explanation

The charge stored on a capacitor is given by Q = CV. Substituting C = 10 μF and V = 12 V gives Q = 120 μC.

Question 48Physics

A 60 kg student stands on a bathroom scale in an elevator that is accelerating upward at 2.0 m/s². Using g = 9.8 m/s², what does the scale read?

  1. 120 N
  2. 480 N
  3. 588 N
  4. 708 N Correct answer.

Explanation

The scale reads the normal force, and Newton's second law for the upward acceleration is N − mg = ma. Thus N = m(g + a) = 60 kg × 11.8 m/s² ≈ 708 N.

Question 49Physics

A 1000 kg car travels at a constant speed of 10 m/s around a horizontal circular curve of radius 50 m. What is the magnitude of the centripetal force on the car?

  1. 2000 N Correct answer.
  2. 10000 N
  3. 200 N
  4. 5000 N

Explanation

Centripetal force has magnitude F_c = mv²/r. Substituting gives 1000 kg × (10 m/s)² / 50 m = 2000 N.

Question 50Physics

How much heat must be added to 0.20 kg of ice at 0°C to melt it completely into water at 0°C? The latent heat of fusion of water is 3.34 × 10^5 J/kg.

  1. 3.34 × 10^5 J
  2. 6.68 × 10^4 J Correct answer.
  3. 6.68 × 10^5 J
  4. 1.67 × 10^4 J

Explanation

Melting at constant temperature requires Q = mL_f. Thus Q = 0.20 kg × 3.34 × 10^5 J/kg = 6.68 × 10^4 J.