Angola 12th Grade National Examination — Physics (Física)

A vehicle traveling along a straight horizontal road accelerates uniformly from an initial velocity of 10 m/s to a final velocity of 30 m/s over a displacement of 100 m. What is the magnitude of the vehicle's constant acceleration?

• A4.0 m/s^2
• B2.0 m/s^2
• C5.0 m/s^2
• D8.0 m/s^2

A projectile is launched horizontally with an initial speed of 20 m/s from the edge of a cliff 45 m above flat ground. Neglecting air resistance and taking g = 10 m/s^2, what is the horizontal distance (range) traveled by the projectile before impact?

• A45 m
• B60 m
• C90 m
• D120 m

A soccer ball is kicked from ground level with an initial velocity of 40 m/s at an angle of 30° above the horizontal. Taking g = 10 m/s^2 and sin(30°) = 0.50, what maximum vertical height does the ball reach above the ground?

• A15 m
• B40 m
• C20 m
• D80 m

A block of mass 5.0 kg rests on a frictionless horizontal floor. A pulling force of magnitude F = 25 N is applied at an angle of 37° above the horizontal. Given cos(37°) = 0.80 and sin(37°) = 0.60, what is the horizontal acceleration of the block?

• A3.0 m/s^2
• B6.25 m/s^2
• C5.0 m/s^2
• D4.0 m/s^2

A block of mass 4.0 kg is placed at rest on an inclined plane making an angle of 30° with the horizontal. The coefficient of static friction between the block and the plane is μ_s = 0.60. Taking g = 10 m/s^2, sin(30°) = 0.50, and cos(30°) = 0.87, which statement correctly describes the friction force acting on the block?

• AThe block remains stationary, and the static friction force is exactly 20 N acting up the…
• BThe block slides down the incline because the downhill gravitational component exceeds ma…
• CThe block remains stationary, and the static friction force is 20.88 N acting up the incl…
• DThe static friction force is zero because the block is at rest.

A textbook of mass 2.0 kg is held stationary against a vertical wall by applying a horizontal force F perpendicular to the wall. The coefficient of static friction between the book and the wall is μ_s = 0.40. Taking g = 10 m/s^2, what is the minimum horizontal force F required to prevent the book from slipping downward?

• A8.0 N
• B50 N
• C20 N
• D80 N

In an ideal Atwood machine, two masses m_1 = 3.0 kg and m_2 = 2.0 kg are connected by a light inextensible string passing over a frictionless, massless pulley. Taking g = 10 m/s^2, what is the magnitude of the acceleration of the system?

• A1.0 m/s^2
• B4.0 m/s^2
• C2.0 m/s^2
• D5.0 m/s^2

A car of mass 1200 kg negotiates an unbanked circular curve of radius R = 80 m on a flat horizontal road at a constant speed of 20 m/s. Taking g = 10 m/s^2, what is the minimum coefficient of static friction μ_s required between the tires and the road to prevent the car from skidding?

• A0.25
• B0.80
• C0.65
• D0.50

A highway curve of radius R = 150 m is engineered for a design speed of v = 30 m/s (108 km/h). What is the ideal banking angle θ of the road such that a vehicle can negotiate the turn safely even in the complete absence of friction? (Take g = 10 m/s^2)

• Aθ = arctan(0.60)
• Bθ = arctan(0.45)
• Cθ = arctan(0.20)
• Dθ = arctan(0.75)

A horse pulls a cart forward along a level road. According to Newton's third law, the cart exerts an equal and opposite force backward on the horse. Why does the horse-cart system accelerate forward?

• AThe horse pulls the cart slightly before the cart pulls back, creating a brief net forwar…
• BThe action and reaction forces act on different bodies (horse on cart, cart on horse), wh…
• CThe horse is more massive than the cart, so its inertia overcomes the reaction force.
• DNewton's third law only applies to static systems, not to accelerating systems.

Block A of mass m_A = 6.0 kg rests on a rough horizontal table with kinetic friction coefficient μ_k = 0.25. It is connected by a light string over a frictionless pulley to hanging block B of mass m_B = 4.0 kg. Taking g = 10 m/s^2, what is the acceleration of the system once released?

• A1.5 m/s^2
• B3.5 m/s^2
• C2.5 m/s^2
• D4.0 m/s^2

The velocity-time graph of an object moving in a straight line forms a trapezoid: it accelerates uniformly from rest to 12 m/s in 4.0 s, maintains 12 m/s for 6.0 s (from t = 4.0 s to t = 10.0 s), and then decelerates uniformly to rest in 4.0 s (from t = 10.0 s to t = 14.0 s). What is the total displacement over the 14.0-second interval?

• A96 m
• B168 m
• C144 m
• D120 m

When a skydiver falls through the atmosphere and reaches terminal velocity, which of the following statements is physically true?

• AThe upward aerodynamic drag force equals the downward gravitational force, resulting in z…
• BThe gravitational force is zero because the skydiver is in free fall.
• CThe drag force of the air is zero because the speed is constant.
• DThe acceleration of the skydiver equals 9.8 m/s^2 downward.

A person of mass 70 kg stands on a bathroom scale calibrated in Newtons inside an elevator. If the elevator accelerates upward at a constant rate of a = 2.0 m/s^2, what value does the scale read? (Take g = 9.8 m/s^2)

• A546 N
• B826 N
• C686 N
• D980 N

A motorboat heads directly across a river of width 120 m with a speed of 4.0 m/s relative to the water, pointing perpendicular to the riverbanks. The river current flows downstream at 3.0 m/s. How far downstream from its intended landing point directly across the river will the boat arrive on the opposite bank?

• A60 m
• B120 m
• C90 m
• D150 m

An ideal spring with spring constant k = 500 N/m is compressed by 0.20 m from its relaxed equilibrium position. How much work was done by the external compressing force on the spring?

• A5.0 J
• B100 J
• C50 J
• D10 J

A car of mass 1000 kg traveling at 20 m/s is brought to a complete stop by emergency braking. According to the work-kinetic energy theorem, what is the total work done by the braking friction force on the car?

• A-200 kJ
• B-100 kJ
• C-400 kJ
• D-20 kJ

A roller coaster car travels around the inside of a vertical circular loop of radius R = 10 m. What is the theoretical minimum speed the car must have at the very top of the loop so that it maintains contact with the track without falling? (Take g = 10 m/s^2)

• A5.0 m/s
• B10 m/s
• C14 m/s
• D20 m/s

A construction crane lifts a load of mass 1500 kg vertically upward through a height of 20 m at a constant speed in a time of 30 s. Taking g = 10 m/s^2, what average mechanical power is developed by the crane motor?

• A5.0 kW
• B15 kW
• C10 kW
• D30 kW

A baseball of mass 0.15 kg traveling horizontally at 40 m/s is struck by a bat and rebounds in the exact opposite direction at 50 m/s. If the bat and ball remain in contact for 0.0050 s, what is the magnitude of the average force exerted by the bat on the ball?

• A300 N
• B1350 N
• C5400 N
• D2700 N

A glider of mass m_1 = 2.0 kg moving along a frictionless linear air track at 6.0 m/s undergoes a completely inelastic collision with a stationary glider of mass m_2 = 4.0 kg. How much mechanical kinetic energy is converted into thermal energy/deformation during the collision?

• A24 J
• B12 J
• C36 J
• D48 J

Sphere A of mass m moving with speed v_0 along a frictionless surface makes a head-on, perfectly elastic collision with stationary Sphere B of mass 3m. What are the velocities of Sphere A (v_Af) and Sphere B (v_Bf) immediately after the collision?

• Av_Af = 0 and v_Bf = +v_0 / 3
• Bv_Af = -0.50 v_0 and v_Bf = +0.50 v_0
• Cv_Af = -0.25 v_0 and v_Bf = +0.75 v_0
• Dv_Af = +0.50 v_0 and v_Bf = +0.50 v_0

Two identical pucks of mass 0.50 kg slide on a frictionless ice table. Puck 1 moves east at 4.0 m/s and puck 2 moves north at 3.0 m/s. They collide and stick together. What is the speed of the combined mass immediately after the collision?

• A5.0 m/s
• B3.5 m/s
• C2.5 m/s
• D7.0 m/s

In a ballistic pendulum experiment, a bullet of mass m = 0.020 kg is fired horizontally into a wooden block of mass M = 1.98 kg suspended by light cords. The bullet embeds into the block, and the combined system swings upward to a maximum vertical height of h = 0.20 m. Taking g = 10 m/s^2, what was the initial speed of the bullet?

• A100 m/s
• B400 m/s
• C300 m/s
• D200 m/s

A mass m = 0.50 kg attached to an ideal horizontal spring with spring constant k = 200 N/m executes Simple Harmonic Motion (SHM) on a frictionless surface. What is the angular frequency ω of the oscillation?

• A20 rad/s
• B10 rad/s
• C100 rad/s
• D400 rad/s

A simple pendulum on Earth has a length of L = 0.98 m. Taking g = 9.8 m/s^2 and π ≈ 3.14, what is the period T of small-angle oscillations of the pendulum?

• A1.0 s
• B2.0 s
• C3.14 s
• D6.28 s

An object executing simple harmonic motion has amplitude A. When the object's displacement from the equilibrium position is x = A / 2, what percentage of the total mechanical energy is in the form of kinetic energy?

• A25%
• B50%
• C75%
• D87%

In a forced mechanical oscillator subjected to a periodic driving force of frequency f_d, what physical condition produces the phenomenon of resonance?

• AThe damping coefficient must be greater than the critical damping value.
• BThe potential energy of the system must permanently drop to zero.
• CThe amplitude of the driving force must approach zero.
• DThe driving frequency f_d must equal or be very close to the natural frequency f_0 of the…

Two uniform lead spheres, each of mass m = 1000 kg, are placed so that their centers of mass are separated by a distance of r = 2.0 m. Taking the universal gravitational constant G = 6.67 x 10^-11 N·m^2/kg^2, what is the magnitude of the mutual gravitational attraction force between them?

• A1.67 x 10^-5 N
• B3.34 x 10^-5 N
• C6.67 x 10^-5 N
• D1.33 x 10^-4 N

If the acceleration due to gravity at the surface of the Earth (radius R_E) is g_0 = 9.8 m/s^2, what is the gravitational field strength at an altitude of h = R_E above the Earth's surface?

• A1.23 m/s^2
• B2.45 m/s^2
• C4.90 m/s^2
• D9.80 m/s^2

A satellite orbits Earth in a circular Low Earth Orbit at a distance approximately equal to Earth's radius R_E = 6.4 x 10^6 m. Taking Earth's mass M_E = 6.0 x 10^24 kg and G = 6.67 x 10^-11 N·m^2/kg^2, what is the approximate orbital speed v of the satellite?

• A5.6 km/s
• B9.8 km/s
• C7.9 km/s
• D11.2 km/s

An exoplanet orbits a star in a circular orbit with an orbital radius 4 times that of Earth's orbit around the Sun (a = 4 AU). Assuming the host star has the same mass as our Sun, what is the orbital period T of the exoplanet in Earth years?

• A2 years
• B4 years
• C16 years
• D8 years

Kepler's Second Law (Law of Equal Areas) states that a line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time. What fundamental conservation law directly accounts for this planetary behavior?

• AConservation of angular momentum
• BConservation of linear momentum
• CConservation of mechanical energy only
• DConservation of electrical charge

The escape velocity from the surface of a spherical planet of mass M and radius R is given by v_esc = sqrt(2GM / R). If a newly discovered planet has twice the mass of Earth (M_p = 2 M_E) and half the radius of Earth (R_p = 0.5 R_E), what is the escape velocity from this planet in terms of Earth's escape velocity v_E?

• Av_esc = v_E
• Bv_esc = 2 v_E
• Cv_esc = sqrt(2) v_E
• Dv_esc = 4 v_E

Which of the following characteristics uniquely defines a geostationary satellite orbiting the Earth?

• AIt can orbit at any altitude as long as its orbital plane passes through both geographica…
• BIt remains fixed at one position in space while the Earth rotates underneath it.
• CIts orbital period equals Earth's sidereal rotation period (about 23 h 56 min), its orbit…
• DIt moves faster than the speed of light to track the Earth's rotation.

A satellite of mass m moves in a stable circular orbit of radius r around a planet of mass M. What is the relationship between the satellite's kinetic energy K, gravitational potential energy U (with U = 0 at infinity), and total mechanical energy E?

• AE = 0 and U = -K
• BE = +K and U = -K
• CE = -2K and U = -K
• DE = -K and U = -2K

A scuba diver descends to a depth of h = 25 m in seawater (density ρ = 1025 kg/m^3). Taking g = 10 m/s^2 and atmospheric pressure P_atm = 1.00 x 10^5 Pa, what is the total absolute pressure experienced by the diver at this depth?

• A3.56 x 10^5 Pa
• B2.56 x 10^5 Pa
• C4.56 x 10^5 Pa
• D5.12 x 10^5 Pa

In a hydraulic lift operating on Pascal's principle, the small input piston has a cross-sectional area of A_1 = 0.0050 m^2 and the large output piston has an area of A_2 = 0.25 m^2. If an input force of F_1 = 150 N is applied to the small piston, what maximum load force F_2 can the large piston support?

• A1500 N
• B7500 N
• C3750 N
• D15000 N

A solid metal block has a mass of 8.0 kg and a volume of V = 0.0010 m^3 (1.0 L). When completely submerged in water (density ρ_w = 1000 kg/m^3), what is the buoyant force acting on the block, and what is its apparent weight? (Take g = 10 m/s^2)

• ABuoyant force = 1.0 N; Apparent weight = 79 N
• BBuoyant force = 80 N; Apparent weight = 0 N
• CBuoyant force = 10 N; Apparent weight = 70 N
• DBuoyant force = 70 N; Apparent weight = 10 N

An iceberg of density ρ_ice = 920 kg/m^3 floats in ocean water of density ρ_sea = 1000 kg/m^3. What percentage of the total volume of the iceberg remains submerged below the water surface?

• A8.0%
• B46%
• C80%
• D92%

A U-shaped open tube contains water (density ρ_1 = 1.00 g/cm^3). An immiscible oil (density ρ_2 = 0.80 g/cm^3) is poured into the right arm until the oil column reaches a height of h_2 = 20 cm above the interface. What is the height h_1 of the water column in the left arm above the interface level?

• A16 cm
• B12 cm
• C20 cm
• D25 cm

Water flows smoothly through a horizontal cylindrical pipe. In the wide section, the pipe diameter is d_1 = 6.0 cm and the flow speed is v_1 = 1.5 m/s. The pipe constricts to a narrow section of diameter d_2 = 2.0 cm. What is the flow speed v_2 in the constricted section?

• A4.5 m/s
• B13.5 m/s
• C9.0 m/s
• D18.0 m/s

According to Bernoulli's principle for the steady, non-viscous horizontal flow of an incompressible fluid, what happens to the static pressure in regions where the fluid velocity increases?

• AThe static pressure increases proportionally to the square of velocity.
• BThe static pressure remains completely constant.
• CThe static pressure decreases.
• DThe static pressure drops instantaneously to negative infinity.

A large open water storage tank has a small puncture hole in its vertical side at a depth of h = 5.0 m below the free water surface. Applying Torricelli's law and taking g = 9.8 m/s^2, what is the speed at which water squirts out from the hole?

• A4.9 m/s
• B7.0 m/s
• C14.0 m/s
• D9.9 m/s

Water (ρ = 1000 kg/m^3) flows through a horizontal pipe. At Point 1, the speed is v_1 = 2.0 m/s and the pressure is P_1 = 200 kPa. At Point 2 downstream, the pipe narrows and the speed increases to v_2 = 6.0 m/s. What is the static pressure P_2 at Point 2?

• A184 kPa
• B168 kPa
• C200 kPa
• D216 kPa

Why do small liquid droplets (such as dew drops or rain drops in free fall) naturally adopt a spherical geometric shape in the absence of external forces?

• AThe hydrostatic pressure inside the droplet is negative.
• BSurface tension forces act to minimize the liquid's surface area for a given volume, and…
• CExternal atmospheric pressure alone fixes the shape, regardless of the liquid's intermole…
• DThe viscosity of the liquid prevents any non-spherical deformation.

A sample containing 2.0 moles of an ideal gas is enclosed in a rigid container of volume V = 0.050 m^3 at a temperature of T = 300 K. Taking the universal gas constant R = 8.314 J/(mol·K), what is the pressure exerted by the gas?

• A4.99 x 10^4 Pa
• B1.99 x 10^5 Pa
• C9.98 x 10^4 Pa
• D4.99 x 10^5 Pa

What is the root-mean-square (RMS) speed v_rms of nitrogen gas molecules (N_2, molar mass M = 0.028 kg/mol) at an absolute temperature of T = 300 K? (Take R = 8.314 J/(mol·K))

• A258 m/s
• B365 m/s
• C731 m/s
• D517 m/s