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ILTS Science: Physics (243) study materials
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ILTS Science: Physics (243) practice questions

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Question 1Nature of Science and Scientific Inquiry

In physics, which statement best describes the relationship between a scientific theory and a scientific law?

  1. A theory becomes a law once enough experimental evidence has accumulated.
  2. A law explains why phenomena occur, while a theory summarizes observed patterns.
  3. A theory explains why phenomena occur, while a law describes a consistent pattern. Correct answer.
  4. A theory is a tentative guess, while a law is a proven and permanent fact.

Explanation

In science, a theory is an explanatory framework supported by evidence, while a law is a concise description of a regularity. They are different kinds of knowledge, not stages in a hierarchy, so a theory does not become a law when evidence accumulates. This distinction is central in physics, where laws describe patterns and theories explain them.

Question 2Nature of Science and Scientific Inquiry

Which SI unit is correctly expressed as a derived unit in terms of base units?

  1. The kelvin, expressed as kg·m²·s⁻²·K⁻¹
  2. The mole, expressed as mol·L⁻¹
  3. The candela, expressed as cd·sr
  4. The newton, expressed as kg·m·s⁻² Correct answer.

Explanation

The newton is a derived SI unit defined as the force that gives a 1 kg mass an acceleration of 1 m/s², so its base-unit form is kg·m·s⁻². Base units such as the kelvin, mole, and candela are not derived units, even when combined with other units in a particular expression.

Question 3Nature of Science and Scientific Inquiry

A student measures a metal cylinder's length as 12.50 cm and its diameter as 2.0 cm. Using the exact value of π, which reported volume has the correct number of significant figures?

  1. 39 cm³ Correct answer.
  2. 39.27 cm³
  3. 4 × 10¹ cm³
  4. 39.3 cm³

Explanation

The diameter 2.0 cm has two significant figures, so the radius 1.0 cm also has two. Multiplication and division limit the result to the least number of significant figures, giving 39 cm³ with two significant figures. π is an exact factor and does not limit the count.

Question 4Nature of Science and Scientific Inquiry

Four groups use the same balance to find the mass of a 50.00 g standard mass. Which set of results is precise but not accurate?

  1. 49.81 g, 49.80 g, 49.82 g, 49.81 g Correct answer.
  2. 49.98 g, 50.01 g, 50.00 g, 49.99 g
  3. 48.20 g, 51.70 g, 49.10 g, 50.80 g
  4. 49.70 g, 50.30 g, 49.95 g, 50.05 g

Explanation

Precision describes how closely repeated measurements agree with one another, while accuracy describes how close they are to the accepted value. The set in option 3 clusters tightly but is offset from 50.00 g, so it is precise but not accurate.

Question 5Nature of Science and Scientific Inquiry

A student tests whether the angle of a ramp affects the acceleration of a cart. To obtain a valid conclusion about the angle, the student should keep which quantity constant?

  1. The angle of the ramp and the mass of the cart
  2. The time of travel and the acceleration of the cart
  3. The mass of the cart and the surface of the ramp Correct answer.
  4. The acceleration of the cart and the length of the ramp

Explanation

The angle is the independent variable and acceleration is the dependent variable, so all other factors that could affect acceleration must be controlled. Keeping the cart mass and ramp surface constant prevents those variables from confounding the effect of angle.

Question 6Nature of Science and Scientific Inquiry

A value accepted as 9.81 m/s² is measured as 9.45 m/s². What is the percent error, to the appropriate number of significant figures?

  1. 3.67%
  2. 3.8%
  3. 3.7% Correct answer.
  4. 0.037%

Explanation

Percent error is the absolute difference between the measured and accepted values divided by the accepted value, multiplied by 100. The difference 0.36 m/s² has two significant figures, so the result 3.6697% is reported as 3.7%.

Question 7Nature of Science and Scientific Inquiry

In physics research, what is the main function of peer review before a result is published?

  1. It establishes whether the new claim agrees with the current scientific consensus.
  2. It checks whether methods, analysis, and conclusions meet disciplinary standards. Correct answer.
  3. It repeats the experiment in an independent laboratory to verify the result.
  4. It guarantees that the reported measurements are free of random error.

Explanation

Peer review is a disciplinary quality check: reviewers examine whether the experimental design, data analysis, and conclusions are sound and appropriately supported. It does not guarantee error-free data, replicate the work, or require agreement with prevailing views.

Question 8Nature of Science and Scientific Inquiry

A student plots the square of the period, T², versus the length L for a simple pendulum and obtains a straight line through the origin. What does the slope of this graph represent?

  1. The reciprocal of the acceleration due to gravity, 1/g
  2. The acceleration due to gravity, g
  3. Four times the acceleration due to gravity, 4g
  4. The quantity 4π²/g Correct answer.

Explanation

For a simple pendulum, T = 2π√(L/g), so squaring both sides gives T² = (4π²/g)L. A plot of T² versus L therefore has a slope equal to 4π²/g, provided the small-angle approximation holds.

Question 9Nature of Science and Scientific Inquiry

A physics class uses the ideal gas model to predict the pressure of a real gas near its condensation point. The prediction is poor. Which statement best explains the limitation of the model in this situation?

  1. The model neglects intermolecular forces and molecular volume, which become significant near condensation. Correct answer.
  2. The model requires the gas to be monatomic, and most real gases near condensation are diatomic.
  3. The model assumes that gas molecules move at the same speed, which is only true at low pressure.
  4. The model applies only to gases that do not exchange energy in collisions with container walls.

Explanation

The ideal gas model assumes that molecular volume is negligible and that intermolecular forces are zero. Near condensation, molecules are close together and attractive forces matter, so those assumptions fail and the model's pressure prediction becomes unreliable.

Question 10Nature of Science and Scientific Inquiry

A researcher finds that one trial's result is far from the others and excludes it from the analysis without reporting the exclusion. Which practice best describes this action and its main problem?

  1. Replication, because repeating the analysis without the point strengthens the conclusion.
  2. Selective reporting, because excluding data requires a stated objective criterion and disclosure. Correct answer.
  3. Acceptable outlier rejection, because anomalous data are always invalid.
  4. Peer review, because other scientists will detect the missing trial before publication.

Explanation

Outliers may be excluded only when a stated, objective criterion is applied consistently and the exclusion is disclosed. Silent removal of a disagreeing trial is selective reporting, which biases the analysis and undermines reproducibility.

Question 11Nature of Science and Scientific Inquiry

A physics student predicts that increasing the mass of a pendulum bob will not change the pendulum's period. Which feature makes this statement a scientific hypothesis rather than a simple opinion?

  1. It can be tested by experiment and potentially shown false. Correct answer.
  2. It cannot be measured with standard laboratory equipment.
  3. It describes a familiar object using everyday language.
  4. It agrees with what most students already believe about pendulums.

Explanation

A scientific hypothesis is a testable and potentially falsifiable prediction about how variables are related. The statement predicts a specific outcome that can be checked by changing the bob's mass while holding other factors constant.

Question 12Nature of Science and Scientific Inquiry

A student tests how the length of a pendulum affects its period. The student keeps the bob mass and the release angle the same in every trial. In this experiment, the bob mass and release angle are best described as

  1. hypotheses
  2. controlled variables Correct answer.
  3. independent variables
  4. dependent variables

Explanation

Controlled variables are factors deliberately held constant so they cannot confound the relationship being tested. Keeping bob mass and release angle fixed isolates the effect of pendulum length on period.

Question 13Nature of Science and Scientific Inquiry

A student watches a cart roll down a ramp and writes, The cart's acceleration decreased as additional masses were placed on it. Which type of statement is this?

  1. An inference about the motor
  2. A direct observation Correct answer.
  3. A broad scientific theory
  4. A hypothesis about friction

Explanation

An observation describes what is directly measured or perceived, such as a change in acceleration. The statement does not explain why the change occurred, so it is not yet an inference or hypothesis.

Question 14Nature of Science and Scientific Inquiry

A spring scale reads 0.60 N when nothing is attached. Throughout an experiment, every reading is 0.60 N higher than the true force. This error is best classified as

  1. systematic error Correct answer.
  2. random error
  3. precision limitation
  4. calculation mistake

Explanation

Systematic error shifts all measurements in the same direction by a consistent amount, often because of poor calibration or a zero offset. Random error would scatter readings unpredictably around the true value.

Question 15Nature of Science and Scientific Inquiry

A student must measure the thickness of one sheet of paper using a metric ruler marked in millimeters. Which procedure gives the most reliable result?

  1. Measure one sheet and estimate the fraction of a millimeter by eye.
  2. Measure a stack of 100 sheets, then divide by 100. Correct answer.
  3. Measure the sheet's length and width, then multiply them.
  4. Measure one sheet several times and choose the largest reading.

Explanation

Stacking many identical sheets amplifies the total thickness so the ruler's millimeter markings can be used more effectively. Dividing by the number of sheets reduces the relative uncertainty in the single-sheet thickness.

Question 16Nature of Science and Scientific Inquiry

A researcher finds that districts with more physics laboratory equipment also have higher average physics test scores. Which conclusion is best supported by this finding alone?

  1. Test scores cause districts to buy equipment.
  2. The correlation must be due to random error.
  3. An association exists, but causation is not established. Correct answer.
  4. Better equipment causes higher scores.

Explanation

A correlation shows that two variables vary together, but it does not establish which variable, if either, causes the other. Confounding factors such as funding or teacher quality could explain the association.

Question 17Nature of Science and Scientific Inquiry

Two independent laboratories repeat the same physics experiment and obtain results consistent with each other. This outcome most directly supports the

  1. accuracy of each individual instrument
  2. statistical significance of the result
  3. reproducibility of the result Correct answer.
  4. theoretical impossibility of error

Explanation

Reproducibility means independent researchers obtain consistent results using independent experiments or setups. Agreement across laboratories strengthens confidence but does not by itself prove accuracy or statistical significance.

Question 18Nature of Science and Scientific Inquiry

A student plots applied force on the vertical axis versus acceleration on the horizontal axis for a cart. The best-fit line has a small positive vertical intercept. Which interpretation is most reasonable?

  1. A constant offset, such as friction, is present. Correct answer.
  2. The cart's mass changes during each trial.
  3. Random error alone always produces a positive intercept.
  4. Acceleration is independent of applied force.

Explanation

A nonzero intercept suggests a constant additional force or offset not included in the ideal force-versus-acceleration model. Friction or an unzeroed sensor can shift the line upward by a fixed amount.

Question 19Nature of Science and Scientific Inquiry

A physics team reports that a new coating changes measured thermal conductivity by 4%, with a 95% confidence interval of -1% to 9%. Which interpretation is most appropriate?

  1. The coating definitely has no effect on thermal conductivity.
  2. A 95% confidence interval proves the experiment had no systematic error.
  3. The coating definitely increases thermal conductivity by 4%.
  4. The data are compatible with no effect. Correct answer.

Explanation

Because the 95% confidence interval includes zero, the observed 4% change is not distinguishable from no effect at that confidence level. This does not prove the effect is zero; it means the evidence is inconclusive.

Question 20Nature of Science and Scientific Inquiry

New, highly reproducible evidence conflicts with a long-standing physics theory that has already explained many observations. What is the most scientifically appropriate response?

  1. Declare the old theory false immediately and discard all of its predictions.
  2. Test the evidence further and consider revising the theory. Correct answer.
  3. Adjust the new data until they agree with the established theory.
  4. Ignore the new evidence because the theory is established.

Explanation

Scientific theories are revised when new, reliable evidence cannot be accommodated by existing explanations. The appropriate response is further testing, replication, and theoretical revision rather than automatic rejection or data manipulation.

Question 21Nature of Science and Scientific Inquiry

A physics student measures the period of a simple pendulum five times and calculates the average period. Why does averaging repeated trials improve the result?

  1. It increases the resolution of the stopwatch.
  2. It reduces the effect of random error. Correct answer.
  3. It removes every systematic error.
  4. It proves that the hypothesis is true.

Explanation

Random errors vary unpredictably from trial to trial, so averaging a set of independent readings gives a mean that is usually closer to the true value. The process does not correct a consistent offset such as a mis-calibrated stopwatch, and no amount of averaging can prove a hypothesis.

Question 22Nature of Science and Scientific Inquiry

A physics lab reports a length as (2.450 ± 0.003) m. Which statement best describes the meaning of the ±0.003 m?

  1. The measurement has a percent error of exactly 0.003%.
  2. The length is exactly 2.450 m, and 0.003 m is only a significant-figure rounding rule.
  3. It indicates an uncertainty of about 0.003 m around the reported value. Correct answer.
  4. The true length must lie outside the interval 2.447 m to 2.453 m.

Explanation

The ± value is an estimate of the measurement uncertainty, not a guarantee that the true value is exactly the reported number. It defines an interval of about 2.447 m to 2.453 m within which the true value is likely to lie at the stated confidence level.

Question 23Nature of Science and Scientific Inquiry

A student defines 'response time' in an experiment as the time between a light flash and the participant's key press. Why is this operational definition useful in scientific inquiry?

  1. It proves that response time is a fundamental physical quantity.
  2. It guarantees that the measurements contain no uncertainty.
  3. It gives a measurable procedure others can repeat. Correct answer.
  4. It replaces the need for a hypothesis in the experiment.

Explanation

An operational definition translates an abstract concept into a specific measurement procedure, which allows other researchers to replicate the study and compare results. It does not eliminate measurement uncertainty or establish a quantity as fundamental.

Question 24Nature of Science and Scientific Inquiry

A physics collaboration reports a possible new particle with a local significance of 3 sigma. In scientific inquiry, which interpretation is most appropriate?

  1. The excess is certainly caused by an unidentified systematic error in the detector.
  2. The result must be discarded because it has not reached 5 sigma.
  3. The particle's existence has been proven beyond reasonable doubt.
  4. Background is unlikely to explain it, but independent confirmation is needed. Correct answer.

Explanation

A 3-sigma local significance corresponds to a small probability, about 0.3%, that background alone would produce a fluctuation at least this large at that location. It is evidence worth follow-up, not proof, and particle physics generally requires independent data and a more stringent global significance before a discovery claim.

Question 25Mechanics

A cyclist moves along a straight road at a constant velocity of 8 m/s for 12 s. What distance does the cyclist travel?

  1. 144 m
  2. 0.67 m
  3. 96 m Correct answer.
  4. 20 m

Explanation

For motion at constant velocity along a straight line, distance equals speed multiplied by time. Thus d = (8 m/s)(12 s) = 96 m, and no acceleration term is needed.

Question 26Mechanics

A book rests on a table in a classroom. According to Newton's first law, which statement describes the forces on the book?

  1. The gravitational force on the book is greater than the normal force, so it stays down.
  2. The net force on the book is zero, so it remains at rest. Correct answer.
  3. The book remains at rest because no forces act on it.
  4. The table exerts no force on the book because the book is not moving.

Explanation

Newton's first law states that an object at rest remains at rest when the net force on it is zero. The upward normal force balances the downward gravitational force, so the book's acceleration is zero.

Question 27Mechanics

A 4.0 kg crate is pushed 3.0 m across a horizontal floor by a constant horizontal force of 25 N. A kinetic friction force of 7.0 N opposes the motion. What is the net work done on the crate?

  1. 54 J Correct answer.
  2. 75 J
  3. 96 J
  4. 21 J

Explanation

The net horizontal force is 25 N − 7.0 N = 18 N. Net work is net force times displacement, so W_net = (18 N)(3.0 m) = 54 J.

Question 28Mechanics

A 0.50 kg cart moving at 4.0 m/s to the right collides with a stationary 1.5 kg cart on a frictionless track. The carts stick together. What is the velocity of the combined carts immediately after the collision?

  1. 0.50 m/s right
  2. 0.75 m/s right
  3. 1.0 m/s right Correct answer.
  4. 2.0 m/s right

Explanation

Momentum is conserved on a frictionless track: (0.50 kg)(4.0 m/s) = (0.50 kg + 1.5 kg)v. Solving gives v = 1.0 m/s to the right.

Question 29Mechanics

A ball is launched horizontally from a table 1.25 m high with a horizontal speed of 3.0 m/s. Taking g = 10 m/s² and ignoring air resistance, how far from the base of the table does the ball land?

  1. 0.75 m
  2. 1.5 m Correct answer.
  3. 3.0 m
  4. 0.38 m

Explanation

The vertical fall time is t = sqrt(2h/g) = sqrt(2(1.25 m)/(10 m/s²)) = 0.50 s. Horizontal distance is x = v_x t = (3.0 m/s)(0.50 s) = 1.5 m.

Question 30Mechanics

A 0.20 kg ball attached to a string moves in a horizontal circle of radius 0.50 m at a constant speed of 4.0 m/s. What is the magnitude of the centripetal force on the ball?

  1. 6.4 N Correct answer.
  2. 3.2 N
  3. 1.6 N
  4. 12.8 N

Explanation

Centripetal force magnitude is F_c = mv²/r. Substituting gives F_c = (0.20 kg)(4.0 m/s)²/(0.50 m) = 6.4 N.

Question 31Mechanics

A uniform solid disk of mass 2.0 kg and radius 0.30 m rotates about its central axis. A constant tangential force of 3.0 N is applied at the rim. What is the angular acceleration of the disk?

  1. 20 rad/s²
  2. 5.0 rad/s²
  3. 10 rad/s² Correct answer.
  4. 33 rad/s²

Explanation

For a solid disk, I = ½MR² = ½(2.0 kg)(0.30 m)² = 0.090 kg·m². Torque is τ = FR = (3.0 N)(0.30 m) = 0.90 N·m, so α = τ/I = 10 rad/s².

Question 32Mechanics

A satellite orbits Earth in a circular orbit at a radius twice Earth's radius from Earth's center. If the orbital speed at Earth's surface radius would be v, what is the satellite's orbital speed in terms of v?

  1. v
  2. v/√2 Correct answer.
  3. v/2
  4. √2 v

Explanation

Circular orbital speed is v = sqrt(GM/r), so speed scales as 1/sqrt(r). At r = 2R_E, the speed is sqrt(GM/(2R_E)) = v/√2.

Question 33Mechanics

A 10 kg box sits on a horizontal floor. The coefficient of static friction is 0.40 and the coefficient of kinetic friction is 0.25. A horizontal force of 30 N is applied to the box. Taking g = 10 m/s², what is the friction force acting on the box?

  1. 0 N
  2. 30 N Correct answer.
  3. 25 N
  4. 40 N

Explanation

Maximum static friction is μ_s N = (0.40)(10 kg)(10 m/s²) = 40 N. Because the applied 30 N is below this maximum, the box does not slide, and static friction equals 30 N to balance the applied force.

Question 34Mechanics

A mass on a spring undergoes simple harmonic motion with period T. If the mass is doubled while the spring constant remains unchanged, what is the new period?

  1. T/2
  2. √2 T Correct answer.
  3. 2T
  4. T/√2

Explanation

The period of a mass-spring system is T = 2π sqrt(m/k). Doubling m while keeping k fixed multiplies the period by sqrt(2), giving √2 T.

Question 35Mechanics

The SI unit of impulse is equivalent to which of the following units?

  1. J/s
  2. kg·m²/s²
  3. kg·m/s²
  4. kg·m/s Correct answer.

Explanation

Impulse is the product of force and the time interval over which it acts, so its unit is N·s. Because 1 N = 1 kg·m/s², the unit N·s reduces to kg·m/s, the same unit as momentum.

Question 36Mechanics

A student stands on a skateboard and pushes horizontally against a wall. The student then rolls backward. Which statement best explains the student's motion using Newton's laws?

  1. The wall cannot exert a force because it does not move.
  2. The student pushes harder on the wall than the wall pushes back.
  3. The student's inertia decreases as the push is applied.
  4. The wall exerts an equal and opposite force on the student. Correct answer.

Explanation

Newton's third law states that forces occur in equal and opposite pairs acting on different objects. The wall pushes back on the student with the same magnitude of force that the student exerts on the wall, so the student accelerates away from the wall.

Question 37Mechanics

Two small masses are attached to a light rod. A 1.0 kg mass is at x = 0 m, and a 3.0 kg mass is at x = 4.0 m. What is the x-coordinate of the center of mass of the system?

  1. 4.0 m
  2. 3.0 m Correct answer.
  3. 5.0 m
  4. 2.0 m

Explanation

The center of mass is the mass-weighted average position, x_cm = (m1x1 + m2x2)/(m1 + m2). Substituting gives (1.0×0 + 3.0×4.0)/(1.0 + 3.0) = 12/4 = 3.0 m.

Question 38Mechanics

A cart starts from rest and accelerates uniformly at 2.0 m/s² for 5.0 s. It then travels for 3.0 s at the speed it has reached. What is the cart's total displacement during the 8.0 s?

  1. 25 m
  2. 50 m
  3. 30 m
  4. 55 m Correct answer.

Explanation

During the acceleration stage, displacement is (1/2)at² = 0.5(2.0)(5.0)² = 25 m, and final speed is at = 10 m/s. The constant-speed stage adds (10 m/s)(3.0 s) = 30 m, for a total of 55 m.

Question 39Mechanics

A ball is kicked from level ground with an initial speed of 20 m/s at 30° above the horizontal. Ignoring air resistance and using g = 9.8 m/s², what maximum height does the ball reach?

  1. 2.6 m
  2. 1.3 m
  3. 10.2 m
  4. 5.1 m Correct answer.

Explanation

Only the vertical component determines the maximum height: v_y = 20 sin 30° = 10 m/s. Using v_y² = 2gh gives h = (10)²/(2×9.8) ≈ 5.1 m.

Question 40Mechanics

A 2.0 kg block is released from rest at the top of a frictionless incline and descends a vertical height of 1.5 m. What is its speed at the bottom? Use g = 9.8 m/s².

  1. 7.7 m/s
  2. 5.4 m/s Correct answer.
  3. 10.8 m/s
  4. 14.7 m/s

Explanation

Mechanical energy is conserved on a frictionless incline, so mgh = (1/2)mv². The mass cancels, and v = sqrt(2gh) = sqrt(2×9.8×1.5) ≈ 5.4 m/s.

Question 41Mechanics

A 30 kg child sits 1.5 m from the pivot of a balanced seesaw. How far from the pivot must a 45 kg child sit on the opposite side to keep the seesaw balanced?

  1. 2.0 m
  2. 1.5 m
  3. 0.75 m
  4. 1.0 m Correct answer.

Explanation

For rotational balance about the pivot, the torques must have equal magnitudes: m1g r1 = m2g r2. Thus r2 = (30×1.5)/45 = 1.0 m.

Question 42Mechanics

A mass on a spring oscillates with amplitude 0.20 m and angular frequency 6.0 rad/s. What is the maximum speed of the mass?

  1. 1.0 m/s
  2. 1.2 m/s Correct answer.
  3. 0.80 m/s
  4. 0.20 m/s

Explanation

In simple harmonic motion, speed is maximum at the equilibrium position and equals v_max = Aω. Multiplying 0.20 m by 6.0 rad/s gives 1.2 m/s.

Question 43Mechanics

A 0.20 kg ball strikes a smooth wall with a speed of 10 m/s at 45° to the normal. It rebounds with the same speed at 45° to the normal on the other side. What is the magnitude of the impulse exerted by the wall on the ball?

  1. 4.0 N·s
  2. 2.8 N·s Correct answer.
  3. 1.4 N·s
  4. 2.0 N·s

Explanation

For a smooth wall, the tangential velocity is unchanged and the normal component reverses. The normal component changes from -10 cos45° to +10 cos45°, so the impulse magnitude is m(2v cos45°) = 0.20×20×0.707 ≈ 2.8 N·s.

Question 44Mechanics

Two blocks with masses 3.0 kg and 5.0 kg hang from opposite ends of a light string that passes over a frictionless pulley. What is the magnitude of the blocks' acceleration? Use g = 9.8 m/s².

  1. 4.90 m/s²
  2. 2.45 m/s² Correct answer.
  3. 1.23 m/s²
  4. 9.80 m/s²

Explanation

For an Atwood machine, the net driving force is (m2 - m1)g and the total mass accelerated is m1 + m2. Thus a = ((5.0 - 3.0)/(5.0 + 3.0))×9.8 = 2.45 m/s².

Question 45Mechanics

A student walks 6.0 m east and then 8.0 m north. What is the magnitude of the student's resultant displacement from the starting point?

  1. 2.0 m
  2. 14.0 m
  3. 48.0 m
  4. 10.0 m Correct answer.

Explanation

The two displacements are perpendicular, so the resultant magnitude is the hypotenuse: sqrt(6.0^2 + 8.0^2) = 10.0 m. Displacement measures the straight-line change in position from start to finish, not the total path length.

Question 46Mechanics

A 70 kg passenger stands on a scale in an elevator that moves upward at a constant speed. Taking g = 9.8 m/s², what does the scale read?

  1. 0 N
  2. Less than 686 N but not zero
  3. 686 N Correct answer.
  4. More than 686 N

Explanation

At constant velocity the passenger's acceleration is zero, so the net force on the passenger is zero. The scale's normal force must therefore balance the passenger's weight, mg = 70 kg × 9.8 m/s² ≈ 686 N.

Question 47Mechanics

A satellite moves in a circular orbit around Earth. What is the work done by Earth's gravitational force on the satellite during one complete orbit?

  1. Zero, because the force is perpendicular to the velocity Correct answer.
  2. Negative, because gravity continuously pulls the satellite backward
  3. Positive, because gravity continuously pulls the satellite forward
  4. Equal to the gravitational potential energy at that radius

Explanation

Work equals Fd cos θ, and in circular motion the gravitational force is radial while the velocity is tangential, so θ = 90°. Because cos 90° = 0, gravity does zero work over the orbit and the satellite's speed remains constant.

Question 48Mechanics

A 5.0 kg block slides down a 30° incline. The coefficient of kinetic friction between the block and the incline is 0.20. Taking g = 9.8 m/s², what is the block's acceleration down the incline?

  1. 0.98 m/s²
  2. 3.2 m/s² Correct answer.
  3. 4.9 m/s²
  4. 2.5 m/s²

Explanation

The acceleration along an incline with kinetic friction is g(sin θ − μ_k cos θ). Substituting gives 9.8(0.50 − 0.20 × 0.866) ≈ 3.2 m/s² down the incline.

Question 49Mechanics

A 0.15 kg baseball is pitched at 40 m/s and is hit straight back toward the pitcher at 50 m/s. What is the magnitude of the impulse delivered to the ball?

  1. 6.0 N·s
  2. 13.5 N·s Correct answer.
  3. 7.5 N·s
  4. 1.5 N·s

Explanation

Taking the direction away from the pitcher as positive, the change in velocity is 50 m/s − (−40 m/s) = 90 m/s. Impulse magnitude is m|Δv| = 0.15 kg × 90 m/s = 13.5 N·s.

Question 50Mechanics

A 0.50 kg block compresses a spring with spring constant 200 N/m by 0.10 m on a frictionless horizontal surface. The block is released from rest. What is its maximum speed?

  1. 2.0 m/s Correct answer.
  2. 20 m/s
  3. 4.0 m/s
  4. 1.0 m/s

Explanation

The spring's stored potential energy (1/2 kx²) converts entirely into kinetic energy (1/2 mv²) on the frictionless surface. Solving gives v = x√(k/m) = 0.10√(200/0.50) = 2.0 m/s.