Moldova Bacalaureat — Physics (Fizică)

An automobile travels along a straight highway from Chișinău to Bălți, covering a distance of 135 km in exactly 1.5 hours at a constant speed. What is the vehicle's speed expressed in standard SI units (m/s)?

• A15 m/s
• B20 m/s
• C25 m/s
• D30 m/s

A tram departs from rest at a stop and accelerates uniformly in a straight line at a = 1.2 m/s² for a duration of t = 10 s. What distance does the tram cover during this acceleration interval?

• A30 m
• B144 m
• C120 m
• D60 m

A car travelling at an initial velocity of v₀ = 20 m/s brakes with a constant acceleration of magnitude a = 4.0 m/s² until it comes to a complete stop. What is the total stopping distance of the car?

• A25 m
• B40 m
• C50 m
• D80 m

A small metal ball is projected horizontally from the edge of a horizontal table of height h = 1.25 m with an initial horizontal speed of v₀ = 6.0 m/s. Neglecting air resistance and taking g = 10 m/s², what is the horizontal range (distance from the table base to the impact point)?

• A3.0 m
• B1.5 m
• C4.5 m
• D6.0 m

A projectile is launched from ground level with an initial velocity of v₀ = 50 m/s at an angle of θ = 30° above the horizontal. Assuming g = 10 m/s² and negligible air resistance, what is the maximum height H reached by the projectile?

• A15.6 m
• B31.25 m
• C62.5 m
• D125 m

A particle moves along a circular path of radius R = 0.50 m at a constant linear speed of v = 4.0 m/s. What is the magnitude of its centripetal (normal) acceleration?

• A4.0 m/s²
• B8.0 m/s²
• C16 m/s²
• D32 m/s²

A flywheel with a radius of r = 0.25 m rotates uniformly at an angular frequency of n = 120 rpm (revolutions per minute). What is the linear speed of a point located on the outer rim of the flywheel? (Take π ≈ 3.14)

• A1.57 m/s
• B12.56 m/s
• C6.28 m/s
• D3.14 m/s

A net horizontal force of F = 48 N acts on a crate of mass m = 12 kg resting on a frictionless horizontal floor. What is the acceleration produced on the crate?

• A0.25 m/s²
• B2.0 m/s²
• C4.0 m/s²
• D6.0 m/s²

A wooden block of mass m = 5.0 kg is pulled across a horizontal surface by a horizontal force of F = 22 N. The coefficient of kinetic friction between the block and the surface is μ = 0.20. Taking g = 10 m/s², what is the acceleration of the block?

• A2.4 m/s²
• B1.2 m/s²
• C3.6 m/s²
• D4.4 m/s²

A block slides down a smooth, frictionless inclined plane that makes an angle of θ = 30° with the horizontal. Taking g = 10 m/s², what is the acceleration of the block down the incline?

• A2.5 m/s²
• B10.0 m/s²
• C8.66 m/s²
• D5.0 m/s²

A crate of mass m = 10 kg is pushed up an inclined plane angled at θ = 37° above the horizontal at a constant speed by a force F applied parallel to the incline. The coefficient of kinetic friction is μ = 0.25. (Use sin 37° = 0.60, cos 37° = 0.80, and g = 10 m/s²). What is the magnitude of force F?

• A40 N
• B60 N
• C80 N
• D100 N

According to Newton's law of universal gravitation, if the distance between two spherical masses is doubled while both masses remain unchanged, by what factor does the gravitational force between them change?

• AIt decreases by a factor of 4
• BIt decreases by a factor of 2
• CIt increases by a factor of 2
• DIt remains unchanged

An artificial satellite of mass m moves in a stable circular orbit around Earth at an altitude h equal to Earth's radius R (orbit radius r = 2R). If the first cosmic velocity at Earth's surface is v₁ = sqrt(G M / R) ≈ 7.9 km/s, what is the orbital speed v of this satellite?

• Av₁ / sqrt(2)
• Bv₁ / 2
• Cv₁ / 4
• Dv₁ × sqrt(2)

A railway wagon of mass m = 20 tonnes (2.0 × 10⁴ kg) moves along a straight horizontal track at a constant velocity of v = 3.0 m/s. What is the magnitude of the wagon's linear momentum?

• A6.0 × 10³ kg·m/s
• B3.0 × 10⁴ kg·m/s
• C6.0 × 10⁴ kg·m/s
• D1.8 × 10⁵ kg·m/s

A rubber ball of mass m = 0.20 kg travelling horizontally at v₁ = 15 m/s strikes a vertical wall normally and rebounds elastically in the opposite direction at v₂ = 15 m/s. If the impact lasts for Δt = 0.050 s, what is the average force exerted by the wall on the ball?

• A30 N
• B60 N
• C150 N
• D120 N

A cart of mass m₁ = 3.0 kg moving on a frictionless horizontal air track at v₁ = 4.0 m/s collides with and couples (sticks) to a stationary cart of mass m₂ = 5.0 kg. What is the mechanical kinetic energy lost as thermal/internal energy during this completely inelastic collision?

• A9.0 J
• B15.0 J
• C24.0 J
• D33.0 J

A worker pulls a heavy tool chest along a horizontal floor by exerting a constant force of F = 80 N via a strap oriented at θ = 60° above the horizontal. What mechanical work is performed by the worker over a displacement of d = 15 m?

• A400 J
• B600 J
• C1039 J
• D1200 J

An electric crane lifts a concrete slab of mass m = 800 kg vertically at a constant speed of v = 0.75 m/s. Taking g = 9.8 m/s², what is the useful mechanical power output delivered by the crane?

• A5.88 kW
• B3.92 kW
• C7.84 kW
• D9.80 kW

A light horizontal spring with elastic constant k = 500 N/m is compressed by x = 0.20 m against a rigid wall. A block of mass m = 0.20 kg is placed against the compressed spring on a frictionless horizontal table and released from rest. What is the speed of the block as it loses contact with the uncompressed spring?

• A5.0 m/s
• B7.07 m/s
• C10.0 m/s
• D14.1 m/s

How does the period of oscillation T of a simple mathematical pendulum change if its string length L is increased by a factor of 4 while the local gravitational acceleration g remains constant?

• AIt decreases by a factor of 2
• BIt remains unchanged
• CIt increases by a factor of 2
• DIt increases by a factor of 4

A mass-spring oscillator consists of a body of mass m = 0.25 kg attached to an ideal spring with spring constant k = 100 N/m on a frictionless horizontal plane. What is the natural cyclic frequency f of this oscillator? (Take π ≈ 3.14)

• A1.59 Hz
• B20.0 Hz
• C6.28 Hz
• D3.18 Hz

A periodic transverse mechanical wave propagates along a taut wire at a speed of v = 120 m/s. If the source oscillates with a frequency of f = 40 Hz, what is the wavelength λ of the wave?

• A0.33 m
• B1.5 m
• C3.0 m
• D4800 m

A harmonic oscillator of mass m = 0.10 kg undergoes simple harmonic motion described by x(t) = 0.08 cos(25 t) in SI units (where x is in meters and t in seconds). What is the total mechanical energy of the oscillator?

• A0.10 J
• B0.20 J
• C0.40 J
• D0.80 J

An acoustic organ pipe has one closed end and one open end. Its physical length is L = 0.85 m. Taking the speed of sound in air as v = 340 m/s, what is the frequency of the third harmonic (first overtone) produced by this pipe?

• A100 Hz
• B200 Hz
• C300 Hz
• D400 Hz

According to the kinetic-molecular theory of ideal gases, what is the average translational kinetic energy of a molecule in an ideal gas at an absolute temperature of T = 300 K? (Use Boltzmann's constant k = 1.38 × 10⁻²³ J/K)

• A2.07 × 10⁻²¹ J
• B4.14 × 10⁻²¹ J
• C6.21 × 10⁻²¹ J
• D8.28 × 10⁻²¹ J

If the absolute thermodynamic temperature of a sample of neon gas is increased from 100 K to 400 K, by what factor does the root-mean-square speed (v_rms) of its atoms increase?

• A2
• Bsqrt(2)
• C4
• D16

A fixed quantity of an ideal gas occupies a volume of V₁ = 8.0 L at a pressure of p₁ = 1.2 × 10⁵ Pa and temperature T₁ = 300 K. It is heated at constant pressure (isobaric process) until its volume expands to V₂ = 12.0 L. What is the final temperature of the gas?

• A200 K
• B350 K
• C600 K
• D450 K

An airtight, rigid steel cylinder of fixed volume contains an ideal gas at an initial pressure of p₁ = 150 kPa and a temperature of t₁ = 27 °C. The gas is heated until its pressure reaches p₂ = 250 kPa. What is the final temperature in degrees Celsius (°C)?

• A227 °C
• B177 °C
• C45 °C
• D500 °C

During an isothermal compression of an ideal gas at temperature T = const, its volume is reduced from V₁ = 6.0 L to V₂ = 2.0 L. If the initial pressure of the gas was p₁ = 100 kPa, what is the final pressure p₂?

• A33.3 kPa
• B150 kPa
• C200 kPa
• D300 kPa

A storage tank has a volume of V = 0.0831 m³ (83.1 L) and contains oxygen gas (O₂, molar mass M = 32.0 g/mol = 0.032 kg/mol) at a pressure of p = 3.0 × 10⁶ Pa and temperature T = 300 K. Using the universal gas constant R = 8.31 J/(mol·K), what is the mass of oxygen stored in the tank?

• A1.60 kg
• B3.20 kg
• C4.80 kg
• D6.40 kg

The internal energy of a monoatomic ideal gas is given by U = (3/2) ν R T = (3/2) p V. If an ideal monoatomic gas undergoes a transition where its pressure is doubled (p' = 2p) and its volume is simultaneously halved (V' = V/2), how does its internal energy change?

• AIt decreases by half
• BIt remains unchanged (ΔU = 0)
• CIt doubles
• DIt quadruples

An ideal gas inside a cylinder with a movable piston expands isobarically at a constant pressure of p = 2.0 × 10⁵ Pa from an initial volume of V₁ = 0.015 m³ to a final volume of V₂ = 0.045 m³. What work is performed by the expanding gas?

• A3.0 kJ
• B12.0 kJ
• C9.0 kJ
• D6.0 kJ

A sample of an ideal gas enclosed in a rigid container with fixed walls receives Q = 450 J of heat from an external burner. What is the change in the internal energy (ΔU) of the gas?

• A450 J
• B225 J
• C0 J
• D-450 J

A quantity of ν = 2.0 moles of a monoatomic ideal gas is heated isobarically so that its temperature rises by ΔT = 40 K. Taking R = 8.31 J/(mol·K), what total amount of heat Q is absorbed by the gas?

• A665 J
• B997 J
• C2327 J
• D1662 J

An ideal gas expands adiabatically, performing W = 350 J of work against an external load. Which of the following correctly describes the heat exchanged Q and the change in internal energy ΔU of the gas?

• AQ = 350 J and ΔU = 0 J
• BQ = 0 J and ΔU = +350 J
• CQ = 0 J and ΔU = -350 J
• DQ = -350 J and ΔU = 0 J

For an ideal gas, Robert Mayer's relation connects the molar heat capacity at constant pressure (C_p) and constant volume (C_V). What is this fundamental relation?

• AC_p + C_V = R
• BC_p - C_V = R
• CC_p / C_V = R
• DC_V - C_p = R

A working fluid in a heat engine undergoes a closed rectangular cycle on a p-V indicator diagram: state 1 (p₁ = 100 kPa, V₁ = 2.0 m³) -> state 2 (p₂ = 400 kPa, V₂ = 2.0 m³) -> state 3 (p₃ = 400 kPa, V₃ = 5.0 m³) -> state 4 (p₄ = 100 kPa, V₄ = 5.0 m³) -> back to state 1. What is the net mechanical work delivered by the engine in one cycle?

• A300 kJ
• B600 kJ
• C900 kJ
• D1200 kJ

A thermal heat engine absorbs Q_in = 600 J of heat from its hot reservoir during each cycle and exhausts Q_out = 420 J to the cold heat sink. What is the thermal efficiency η of this engine?

• A30%
• B40%
• C50%
• D70%

A Carnot ideal heat engine operates between a heater at temperature T_H = 600 K and a cooler at temperature T_C = 360 K. What is the maximum theoretical efficiency η_Carnot of this engine?

• A25%
• B66.7%
• C60%
• D40%

A Carnot engine operating between temperatures T_H = 800 K and T_C = 300 K receives Q_H = 2000 J of heat from the high-temperature source per cycle. How much heat Q_C is rejected to the cold sink each cycle?

• A750 J
• B500 J
• C1250 J
• D1500 J

What quantity of heat Q is required to completely melt an ice block of mass m = 4.0 kg at its melting temperature of 0 °C? (The specific latent heat of fusion of ice is λ = 3.35 × 10⁵ J/kg).

• A8.38 × 10⁴ J
• B1.34 × 10⁶ J
• C2.68 × 10⁶ J
• D3.35 × 10⁶ J

In a thermally insulated calorimeter, a mass m₁ = 0.30 kg of water at t₁ = 80 °C is mixed with m₂ = 0.20 kg of water at t₂ = 20 °C. Neglecting the heat capacity of the calorimeter vessel and heat loss to the environment, what is the final equilibrium temperature t_f of the mixture?

• A44 °C
• B50 °C
• C62 °C
• D56 °C

A dry steam jet at 100 °C is bubbled into a well-insulated calorimeter containing m_w = 0.45 kg of water at 15 °C. The mixture reaches a final uniform temperature of 35 °C. Taking the specific heat of water c = 4200 J/(kg·°C) and the latent heat of vaporization of water L_v = 2.26 × 10⁶ J/kg, what mass of steam m_s was condensed? (Neglect the calorimeter's heat capacity).

• A10.2 g
• B15.0 g
• C22.5 g
• D37.8 g

Two closed containers at the same temperature contain hydrogen gas (H₂, molar mass M₁ = 2.0 g/mol) and oxygen gas (O₂, molar mass M₂ = 32.0 g/mol), respectively. What is the ratio of the root-mean-square speed of hydrogen molecules to that of oxygen molecules (v_{rms, H₂} / v_{rms, O₂})?

• A1 : 4
• B1 : 16
• C4 : 1
• D16 : 1

A gas mixture inside a rigid vessel contains ν₁ = 3.0 moles of nitrogen (N₂) and ν₂ = 2.0 moles of helium (He). The total pressure exerted by the gas mixture on the vessel walls is p_total = 250 kPa. According to Dalton's law of partial pressures, what is the partial pressure of nitrogen?

• A150 kPa
• B125 kPa
• C100 kPa
• D200 kPa

An aluminum power transmission cable has an initial length of L₀ = 50.0 m at a winter temperature of t₁ = -10 °C. During a summer heatwave, its temperature rises to t₂ = +40 °C. The coefficient of linear thermal expansion for aluminum is α = 2.4 × 10⁻⁵ K⁻¹. What is the elongation ΔL of the cable?

• A3.6 cm
• B24.0 cm
• C12.0 cm
• D6.0 cm

Heat is conducted through a flat glass window pane of thickness d = 5.0 mm (5.0 × 10⁻³ m) and surface area A = 2.0 m². The indoor surface temperature is maintained at 20 °C and the outdoor surface temperature is 0 °C (ΔT = 20 K). The thermal conductivity of glass is k = 0.80 W/(m·K). What is the rate of heat conduction (heat flow power P) through the window?

• A1.6 kW
• B3.2 kW
• C6.4 kW
• D8.0 kW

Which of the following formulations represents the Kelvin-Planck statement of the Second Law of Thermodynamics?

• AHeat can spontaneously transfer from a colder body to a hotter body without any external…
• BIt is impossible to construct a cyclically operating device whose sole effect is to absor…
• CThe total internal energy of an isolated system continuously decreases over time
• DAbsolute zero temperature can be attained in a finite number of thermodynamic operations