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GACE Physics (718) practice questions

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Question 1Mechanics

A student lists four physical quantities: mass, velocity, energy, and momentum. Which of these are vector quantities?

  1. Velocity and momentum Correct answer.
  2. Mass and energy
  3. Mass and velocity
  4. Energy and momentum

Explanation

A vector quantity has both magnitude and direction. Velocity (direction of motion) and momentum (mass times velocity) are vectors. Mass and energy are scalars, having magnitude only.

Question 2Mechanics

A car travels 60 km east, then 80 km north. What is the magnitude of its total displacement?

  1. 100 km Correct answer.
  2. 140 km
  3. 20 km
  4. 70 km

Explanation

Displacement is the straight-line vector from start to finish. With perpendicular legs, the magnitude is sqrt(60^2 + 80^2) = sqrt(3600 + 6400) = sqrt(10000) = 100 km.

Question 3Mechanics

An object starts from rest and accelerates uniformly at 4 m/s^2. How far does it travel in 5 seconds?

  1. 50 m Correct answer.
  2. 20 m
  3. 100 m
  4. 10 m

Explanation

For motion from rest with constant acceleration, x = (1/2)at^2 = (1/2)(4)(5^2) = (1/2)(4)(25) = 50 m. The initial velocity term is zero.

Question 4Mechanics

On a velocity-versus-time graph for an object in motion, what does the area between the curve and the time axis represent?

  1. The displacement of the object Correct answer.
  2. The acceleration of the object
  3. The instantaneous speed
  4. The jerk of the object

Explanation

On a velocity-time graph, the slope gives acceleration and the area under the curve gives displacement, because area equals velocity times time. This is a fundamental graphical relationship in kinematics.

Question 5Mechanics

A projectile is launched horizontally from the top of a cliff. Neglecting air resistance, how does its horizontal velocity component change during flight?

  1. It remains constant Correct answer.
  2. It increases steadily
  3. It decreases to zero at the peak
  4. It first increases then decreases

Explanation

In projectile motion with no air resistance, the only force is gravity, which acts vertically. There is no horizontal force, so the horizontal velocity component stays constant throughout the flight.

Question 6Mechanics

Two observers measure the velocity of a ball thrown inside a train. One stands on the platform; the other rides the train. Their measurements differ because of differences in their:

  1. Frames of reference Correct answer.
  2. Masses
  3. Reaction times
  4. Measuring instruments

Explanation

Velocity is measured relative to a frame of reference. The platform observer measures velocity relative to the ground, while the train observer measures relative to the moving train, so the values differ by the train's velocity.

Question 7Mechanics

According to Newton's first law of motion, an object in motion with no net force acting on it will:

  1. Continue moving at constant velocity Correct answer.
  2. Gradually slow down and stop
  3. Accelerate in the direction of motion
  4. Move in a circular path

Explanation

Newton's first law (the law of inertia) states that an object's velocity remains constant unless acted on by a net external force. With zero net force, a moving object keeps moving in a straight line at constant speed.

Question 8Mechanics

A net force of 12 N acts on a 3 kg object. What is the magnitude of the object's acceleration?

  1. 4 m/s^2 Correct answer.
  2. 36 m/s^2
  3. 9 m/s^2
  4. 0.25 m/s^2

Explanation

Newton's second law gives a = F_net / m = 12 N / 3 kg = 4 m/s^2. Acceleration is directly proportional to net force and inversely proportional to mass.

Question 9Mechanics

A book rests on a table. According to Newton's third law, the reaction force to the gravitational force the Earth exerts on the book is the force:

  1. The book exerts on the Earth Correct answer.
  2. The table exerts on the book
  3. The book exerts on the table
  4. The table exerts on the Earth

Explanation

Newton's third law action-reaction pairs act on different objects and are the same type of force. The reaction to Earth's gravitational pull on the book is the book's equal gravitational pull on the Earth.

Question 10Mechanics

A 10 kg crate sits on a horizontal floor with a coefficient of static friction of 0.40. Using g = 9.8 m/s^2, what is the maximum static friction force before the crate begins to slide?

  1. 39.2 N Correct answer.
  2. 98 N
  3. 4 N
  4. 24.5 N

Explanation

Maximum static friction equals the coefficient times the normal force: f = mu_s * N = 0.40 * (10 kg * 9.8 m/s^2) = 0.40 * 98 N = 39.2 N. On a horizontal surface the normal force equals the weight.

Question 11Mechanics

A car rounds a flat circular curve at constant speed. The direction of the net (centripetal) force on the car points:

  1. Toward the center of the circle Correct answer.
  2. Tangent to the circle in the direction of motion
  3. Outward, away from the center
  4. Vertically downward

Explanation

Uniform circular motion requires a centripetal force directed toward the center of the circular path. For a car on a flat curve, friction supplies this inward force, changing the direction of velocity while keeping speed constant.

Question 12Mechanics

A mass on a spring undergoes simple harmonic motion. At which point in its oscillation is the restoring force greatest?

  1. At maximum displacement from equilibrium Correct answer.
  2. At the equilibrium position
  3. Halfway between equilibrium and maximum displacement
  4. The restoring force is constant throughout

Explanation

By Hooke's law, the restoring force F = -kx is proportional to displacement. The force is therefore largest in magnitude at maximum displacement (the amplitude) and zero at the equilibrium position.

Question 13Mechanics

According to Newton's law of universal gravitation, if the distance between two masses is doubled, the gravitational force between them becomes:

  1. One-fourth as large Correct answer.
  2. One-half as large
  3. Twice as large
  4. Four times as large

Explanation

Gravitational force follows an inverse-square law, F = G m1 m2 / r^2. Doubling r multiplies the denominator by 2^2 = 4, so the force drops to one-fourth of its original value.

Question 14Mechanics

An astronaut has a mass of 80 kg. Compared with values on Earth, on the Moon the astronaut's:

  1. Mass stays the same but weight decreases Correct answer.
  2. Both mass and weight decrease
  3. Mass decreases but weight stays the same
  4. Both mass and weight stay the same

Explanation

Mass is the amount of matter and does not depend on location, so it remains 80 kg. Weight is the gravitational force (W = mg), and because the Moon's g is about one-sixth of Earth's, weight decreases.

Question 15Mechanics

Kepler's second law states that a planet sweeps out equal areas in equal times. This implies that a planet moves:

  1. Fastest when nearest the Sun Correct answer.
  2. Fastest when farthest from the Sun
  3. At constant speed throughout its orbit
  4. In a perfectly circular orbit

Explanation

Kepler's second law (the law of equal areas) is a consequence of conservation of angular momentum. To sweep equal areas in equal times, a planet must move faster when it is closer to the Sun (at perihelion) and slower when farther away.

Question 16Mechanics

A solid steel ball is lowered into water. The upward buoyant force on the ball equals the weight of:

  1. The water displaced by the ball Correct answer.
  2. The steel ball itself
  3. The water above the ball
  4. The container holding the water

Explanation

Archimedes' principle states that the buoyant force on a submerged object equals the weight of the fluid it displaces. This depends on the object's volume and the fluid density, not on the object's own weight.

Question 17Mechanics

Air flowing over the curved top of an airplane wing moves faster than air beneath it. By Bernoulli's principle, this produces lift because faster-moving air has:

  1. Lower pressure Correct answer.
  2. Higher pressure
  3. Greater density
  4. Higher temperature

Explanation

Bernoulli's principle relates fluid speed and pressure: where a fluid moves faster, its pressure is lower. The faster air above the wing creates lower pressure on top, and the higher pressure below pushes the wing upward, generating lift.

Question 18Mechanics

A 2 kg object moving at 3 m/s has how much kinetic energy?

  1. 9 J Correct answer.
  2. 6 J
  3. 18 J
  4. 3 J

Explanation

Kinetic energy is KE = (1/2)mv^2 = (1/2)(2 kg)(3 m/s)^2 = (1/2)(2)(9) = 9 J. Kinetic energy depends on the square of speed.

Question 19Mechanics

A 50 kg student climbs a staircase of vertical height 4 m in 10 seconds. Using g = 9.8 m/s^2, what is the student's average power output?

  1. 196 W Correct answer.
  2. 1960 W
  3. 20 W
  4. 490 W

Explanation

Power is work per unit time. The work done against gravity is W = mgh = 50 * 9.8 * 4 = 1960 J. Power = W / t = 1960 J / 10 s = 196 W.

Question 20Mechanics

A simple machine such as a lever or pulley system can provide a mechanical advantage. Ideally, what does a frictionless machine do to the work output compared with the work input?

  1. Keeps work output equal to work input Correct answer.
  2. Increases the total work done
  3. Decreases the total work done
  4. Eliminates the need for an input force

Explanation

An ideal (frictionless) machine conserves energy, so work output equals work input. The machine can multiply force at the expense of distance, but it cannot create energy; mechanical advantage trades force for displacement.

Question 21Mechanics

A 1500 kg car traveling at 20 m/s comes to a stop. What is the magnitude of the impulse delivered to the car by the braking force?

  1. 30,000 kg*m/s Correct answer.
  2. 75 kg*m/s
  3. 1500 kg*m/s
  4. 300,000 kg*m/s

Explanation

Impulse equals the change in momentum: J = delta p = m * delta v = 1500 kg * (20 - 0) m/s = 30,000 kg*m/s. The impulse-momentum theorem relates the impulse to the momentum change.

Question 22Mechanics

Two ice skaters of equal mass push off from each other while at rest on frictionless ice. After pushing off, the total momentum of the two-skater system is:

  1. Zero, the same as before they pushed off Correct answer.
  2. Doubled compared with before
  3. Equal to the momentum of one skater
  4. Directed toward the heavier skater

Explanation

With no external horizontal force, momentum is conserved. The system started at rest with zero total momentum, so after pushing off the skaters move in opposite directions with equal and opposite momenta that still sum to zero.

Question 23Mechanics

In a perfectly inelastic collision between two objects, which quantity is always conserved?

  1. Linear momentum Correct answer.
  2. Kinetic energy
  3. Both momentum and kinetic energy
  4. Neither momentum nor kinetic energy

Explanation

Momentum is conserved in all collisions when no external forces act. In a perfectly inelastic collision the objects stick together and some kinetic energy is converted to heat and deformation, so kinetic energy is not conserved.

Question 24Mechanics

A figure skater pulls her arms inward while spinning, decreasing her moment of inertia. Because angular momentum is conserved, her angular velocity will:

  1. Increase Correct answer.
  2. Decrease
  3. Remain unchanged
  4. Drop to zero

Explanation

Angular momentum L = I*omega is conserved when no external torque acts. Reducing the moment of inertia I by pulling the arms in requires the angular velocity omega to increase so the product remains constant.

Question 25Mechanics

A force is applied to a wrench to loosen a bolt. To maximize the torque for a given force, the force should be applied:

  1. As far from the bolt as possible and perpendicular to the wrench Correct answer.
  2. As close to the bolt as possible
  3. Along the length of the wrench toward the bolt
  4. At a 45-degree angle near the bolt

Explanation

Torque equals force times lever arm times the sine of the angle (tau = rF sin theta). Torque is maximized by using the longest lever arm (far from the pivot) and applying the force perpendicular (theta = 90 degrees, sin = 1) to the wrench.

Question 26Mechanics

A ball is thrown straight up and returns to the thrower's hand. Neglecting air resistance, at the highest point of its flight, the ball's velocity and acceleration are, respectively:

  1. Zero and 9.8 m/s^2 downward Correct answer.
  2. Zero and zero
  3. 9.8 m/s^2 upward and zero
  4. Zero and 9.8 m/s^2 upward

Explanation

At the peak the ball momentarily stops, so its velocity is zero. Gravity still acts the entire time, so the acceleration remains 9.8 m/s^2 directed downward even at the highest point.

Question 27Mechanics

A 5 kg block is pushed across a horizontal floor at constant velocity by a 15 N horizontal force. What is the magnitude of the kinetic friction force on the block?

  1. 15 N Correct answer.
  2. 5 N
  3. 49 N
  4. 75 N

Explanation

Constant velocity means zero acceleration, so the net force is zero. The kinetic friction force must therefore exactly balance the applied force, giving 15 N opposing the motion.

Question 28Mechanics

A pendulum's period depends on its length and the local acceleration due to gravity. If the length of a simple pendulum is quadrupled, its period will:

  1. Double Correct answer.
  2. Quadruple
  3. Halve
  4. Remain unchanged

Explanation

The period of a simple pendulum is T = 2*pi*sqrt(L/g). Because the period depends on the square root of length, quadrupling L multiplies the period by sqrt(4) = 2, so the period doubles.

Question 29Mechanics

A 0.2 kg ball moving at 5 m/s strikes a wall and rebounds at 5 m/s in the opposite direction. What is the magnitude of the change in the ball's momentum?

  1. 2 kg*m/s Correct answer.
  2. 0 kg*m/s
  3. 1 kg*m/s
  4. 5 kg*m/s

Explanation

Momentum is a vector. Taking the initial direction as positive, the change is delta p = m(v_f - v_i) = 0.2(-5 - 5) = -2 kg*m/s, so the magnitude is 2 kg*m/s. The reversal of direction doubles the speed change.

Question 30Mechanics

A roller coaster car of mass m starts from rest at the top of a frictionless hill of height h. Using energy conservation, its speed at the bottom of the hill is:

  1. sqrt(2gh) Correct answer.
  2. 2gh
  3. sqrt(gh)
  4. mgh

Explanation

With no friction, gravitational potential energy converts entirely to kinetic energy: mgh = (1/2)mv^2. Solving for v gives v = sqrt(2gh); the mass cancels out.

Question 31Thermal Physics

According to kinetic molecular theory, the absolute temperature of an ideal gas is directly proportional to the average:

  1. Translational kinetic energy of its molecules Correct answer.
  2. Potential energy of its molecules
  3. Mass of its molecules
  4. Volume occupied by its molecules

Explanation

Kinetic molecular theory establishes that the absolute (Kelvin) temperature of an ideal gas is directly proportional to the average translational kinetic energy of its molecules. Higher temperature means faster average molecular motion.

Question 32Thermal Physics

Which statement correctly distinguishes heat from temperature?

  1. Heat is energy transferred due to a temperature difference; temperature measures average molecular kinetic energy Correct answer.
  2. Heat and temperature are two names for the same quantity
  3. Temperature is energy in transit; heat is a measure of internal energy
  4. Heat is measured in kelvins; temperature is measured in joules

Explanation

Heat is thermal energy that flows from a hotter object to a cooler one because of a temperature difference, measured in joules. Temperature measures the average kinetic energy of molecules and is measured in kelvins or degrees.

Question 33Thermal Physics

How much heat is required to raise the temperature of 2 kg of water by 10 degrees Celsius? (Specific heat of water = 4186 J/(kg*degC))

  1. 83,720 J Correct answer.
  2. 8,372 J
  3. 41,860 J
  4. 20,930 J

Explanation

Heat is calculated with Q = mc(delta T) = 2 kg * 4186 J/(kg*degC) * 10 degC = 83,720 J. The specific heat tells how much energy each kilogram needs per degree.

Question 34Thermal Physics

A metal spoon placed in hot soup becomes warm at the handle even though only the bowl end is submerged. This transfer of heat through the solid metal is an example of:

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

Explanation

Conduction is heat transfer through direct molecular contact within a material, without bulk movement of the material. Energy passes from the hot end of the spoon to the cooler handle through vibrating, colliding particles.

Question 35Thermal Physics

On a heating curve for water, the temperature remains constant while the substance changes from liquid to gas. During this plateau, the added heat is used to:

  1. Break intermolecular bonds during the phase change Correct answer.
  2. Increase the average kinetic energy of the molecules
  3. Raise the temperature of the steam
  4. Compress the substance into a smaller volume

Explanation

During a phase change the temperature stays constant because the added energy (latent heat of vaporization) goes into overcoming intermolecular attractions rather than raising kinetic energy. Only after the phase change is complete does temperature rise again.

Question 36Thermal Physics

For a fixed amount of ideal gas at constant temperature, if the volume is halved, the pressure will:

  1. Double Correct answer.
  2. Halve
  3. Remain the same
  4. Quadruple

Explanation

At constant temperature, Boyle's law states PV = constant, so pressure and volume are inversely proportional. Halving the volume doubles the pressure.

Question 37Thermal Physics

The first law of thermodynamics is a statement of the conservation of energy. It states that the change in a system's internal energy equals:

  1. The heat added to the system minus the work done by the system Correct answer.
  2. The heat added plus the work done by the system
  3. The work done by the system minus the heat added
  4. Only the heat added to the system

Explanation

The first law is delta U = Q - W, where Q is heat added to the system and W is work done by the system. Internal energy increases when heat is added and decreases when the system does work on its surroundings.

Question 38Thermal Physics

The second law of thermodynamics implies that in any spontaneous, isolated process, the total entropy of the system and surroundings tends to:

  1. Increase Correct answer.
  2. Decrease
  3. Remain exactly constant
  4. Become zero

Explanation

The second law states that the total entropy (disorder) of an isolated system never decreases for spontaneous processes; it increases or, for an idealized reversible process, stays constant. Real spontaneous processes increase total entropy.

Question 39Thermal Physics

A Carnot heat engine operates between a hot reservoir at 600 K and a cold reservoir at 300 K. What is its maximum theoretical efficiency?

  1. 50% Correct answer.
  2. 100%
  3. 25%
  4. 75%

Explanation

Carnot efficiency is e = 1 - (T_cold / T_hot) with temperatures in kelvins: e = 1 - (300/600) = 1 - 0.5 = 0.5, or 50%. This is the theoretical maximum for any engine between these temperatures.

Question 40Modern Physics

Two atoms of the same element have the same number of protons but different numbers of neutrons. These atoms are best described as:

  1. Isotopes Correct answer.
  2. Ions
  3. Isomers
  4. Allotropes

Explanation

Isotopes are atoms of the same element (same proton number) that differ in neutron number, and therefore in mass number. Carbon-12 and carbon-14 are common examples.

Question 41Modern Physics

Rutherford's gold-foil experiment, in which a few alpha particles were deflected at large angles, provided evidence that the atom contains:

  1. A small, dense, positively charged nucleus Correct answer.
  2. A uniform distribution of positive charge
  3. Electrons embedded in a positive pudding
  4. Only neutral particles

Explanation

Most alpha particles passed straight through the foil, but a few bounced back at large angles. Rutherford concluded the atom's positive charge and most of its mass are concentrated in a tiny dense nucleus, with electrons in the surrounding empty space.

Question 42Modern Physics

In the Bohr model of the hydrogen atom, an electron emits a photon of light when it:

  1. Transitions from a higher to a lower energy level Correct answer.
  2. Transitions from a lower to a higher energy level
  3. Remains in a stable orbit
  4. Is removed from the atom entirely

Explanation

In the Bohr model, energy levels are quantized. When an electron drops from a higher level to a lower one, the energy difference is released as a photon whose frequency corresponds to that energy gap, producing an emission line.

Question 43Modern Physics

An emission spectrum from a hot gas appears as bright lines at specific wavelengths rather than a continuous band. These discrete lines occur because:

  1. Electrons occupy discrete, quantized energy levels Correct answer.
  2. The gas atoms move at a single fixed speed
  3. Light slows down inside the gas
  4. The gas absorbs all wavelengths equally

Explanation

Atoms have quantized energy levels, so electron transitions release photons of only specific energies (and thus wavelengths). This produces a line spectrum unique to each element, used to identify gases.

Question 44Modern Physics

In alpha decay, an unstable nucleus emits an alpha particle. The atomic number of the resulting nucleus:

  1. Decreases by 2 Correct answer.
  2. Increases by 2
  3. Decreases by 4
  4. Stays the same

Explanation

An alpha particle is a helium nucleus containing 2 protons and 2 neutrons. Emitting it reduces the parent's atomic number by 2 and its mass number by 4, transforming it into a different element.

Question 45Modern Physics

A radioactive isotope has a half-life of 8 days. Starting with 80 grams, how much remains after 24 days?

  1. 10 grams Correct answer.
  2. 20 grams
  3. 5 grams
  4. 40 grams

Explanation

24 days is three half-lives (24 / 8 = 3). The amount halves each half-life: 80 -> 40 -> 20 -> 10 grams. After three half-lives, one-eighth of the original remains.

Question 46Modern Physics

Nuclear fission and nuclear fusion both release energy. The key difference is that fission involves:

  1. Splitting a heavy nucleus into lighter nuclei, while fusion combines light nuclei Correct answer.
  2. Combining light nuclei, while fusion splits heavy nuclei
  3. Only the emission of alpha particles
  4. No change in nuclear mass

Explanation

Fission splits a heavy nucleus (such as uranium-235) into lighter fragments, releasing energy. Fusion joins light nuclei (such as hydrogen isotopes) into a heavier one, which powers the Sun. Both convert a small mass into energy via E = mc^2.

Question 47Modern Physics

The photoelectric effect demonstrates that electrons are ejected from a metal only when the incident light exceeds a certain threshold frequency. This supports the idea that light:

  1. Behaves as discrete packets of energy called photons Correct answer.
  2. Is purely a continuous wave with no particle nature
  3. Always travels slower than its vacuum speed
  4. Carries energy proportional to its intensity alone

Explanation

Einstein explained the photoelectric effect by treating light as photons whose energy E = hf depends on frequency. Below the threshold frequency, no single photon has enough energy to eject an electron, regardless of intensity, demonstrating light's particle nature.

Question 48Modern Physics

Which phenomenon is the strongest evidence for the wave nature of particles such as electrons?

  1. Electron diffraction Correct answer.
  2. The photoelectric effect
  3. Blackbody radiation
  4. Radioactive decay

Explanation

Electron diffraction shows that electrons produce interference and diffraction patterns like waves, confirming de Broglie's hypothesis that matter has wave properties. This is the clearest evidence for wave-particle duality of matter.

Question 49Modern Physics

Einstein's mass-energy equivalence, E = mc^2, indicates that in a nuclear reaction the energy released comes from:

  1. A small decrease in the total rest mass of the system Correct answer.
  2. An increase in the temperature of the nuclei
  3. The conversion of charge into energy
  4. The destruction of protons into pure light

Explanation

In nuclear reactions, the products have slightly less total rest mass than the reactants. This mass defect is converted into energy according to E = mc^2, releasing the enormous energies seen in fission and fusion.

Question 50Modern Physics

Heisenberg's uncertainty principle states that it is impossible to simultaneously know with perfect precision a particle's:

  1. Position and momentum Correct answer.
  2. Mass and charge
  3. Energy and electric field
  4. Velocity and temperature

Explanation

The Heisenberg uncertainty principle states there is a fundamental limit to how precisely both the position and momentum of a particle can be known at the same time. Reducing uncertainty in one increases uncertainty in the other.