PAKISTAN NAVY RECRUITMENT
PHYSICS TEST (PART 1) • 100 MCQS
Pakistan Navy Sailor Physics Test Preparation (Part 1)
100 Most Repeated Past Paper Physics Questions for Technical Sailor, Marine Sailor, Medical Sailor/FMT, Marine Engineering (ME) and Weapon Engineering (WE). Practice kinematics, dynamics, buoyancy, fluid pressure, thermodynamics, acoustics, sonar, optics, and electromagnetism with instant interactive feedback.
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1
Which of the following is a fundamental base unit in the International System of Units (SI)?
Explanation: Kelvin (K) is one of the seven base SI units for thermodynamic temperature. Newton, Joule, and Pascal are derived units.
2
What is the SI unit of luminous intensity used in optical and maritime signaling devices?
Explanation: The SI base unit of luminous intensity is the candela (cd), measuring light emitted in a particular direction.
3
Which quantity among the following is a vector quantity?
Explanation: Magnetic field intensity has both magnitude and direction, making it a vector quantity. Pressure, resistance, and specific heat are scalars.
4
What is the dimensional formula for mechanical impulse (Impulse = Force * time)?
Explanation: Impulse has dimensions of momentum: [M L T^-2] * [T] = [M L T^-1].
5
If a vernier caliper has a main scale divided in millimeters and 20 vernier divisions coincide with 19 mm, what is its least count?
Explanation: Least count = 1 MSD - 1 VSD = 1 mm - (19/20) mm = 1/20 mm = 0.05 mm.
6
What are the dimensions of the universal gravitational constant G?
Explanation: From F = G*(m1*m2)/r^2, G = F*r^2 / (m1*m2) = [M L T^-2][L^2] / [M^2] = [M^-1 L^3 T^-2].
7
Two vectors of equal magnitude F act perpendicular to each other. What is the magnitude of their resultant?
Explanation: Resultant R = sqrt(F^2 + F^2 + 2*F*F*cos(90 deg)) = sqrt(2*F^2) = F * sqrt(2).
8
Which instrument is used in marine engineering workshops to measure the pitch of small screws and wire gauges with highest precision?
Explanation: A micrometer screw gauge measures diameters and thickness with a least count typically of 0.01 mm or 0.001 cm.
9
What is the angle between two non-zero vectors if their scalar dot product equals the magnitude of their vector cross product?
Explanation: A.B = |A x B| => A*B*cos(theta) = A*B*sin(theta) => tan(theta) = 1 => theta = 45 degrees.
10
One nautical mile corresponds to approximately how many meters?
Explanation: An international nautical mile is defined as exactly 1,852 meters (approx 1.15 statute miles), based on one minute of arc along a meridian.
11
A naval patrol boat decelerates uniformly from 30 m/s to 10 m/s over a distance of 200 meters. What is its acceleration?
Explanation: Using vf^2 = vi^2 + 2*a*s: 10^2 = 30^2 + 2*a*200 => 100 = 900 + 400*a => 400*a = -800 => a = -2.0 m/s^2.
12
The area enclosed under a velocity-time graph represents which physical quantity?
Explanation: The integral/area under a velocity-time graph equals the total displacement traveled by the body.
13
A projectile is launched from a naval vessel deck at an angle of 30 degrees to the horizontal. At what complementary angle will it achieve the same horizontal range?
Explanation: Projectiles launched at complementary angles (theta and 90 - theta) with identical initial speed have the same horizontal range (30 deg and 60 deg).
14
A flare is fired vertically upward with a speed of 49 m/s. What maximum height will it reach? (Take g = 9.8 m/s^2)
Explanation: H_max = vi^2 / (2*g) = (49^2) / (2 * 9.8) = 2401 / 19.6 = 122.5 meters.
15
If an object travels equal distances in equal intervals of time, regardless of how small the intervals are, its motion is described as:
Explanation: Uniform speed implies covering equal distances in equal intervals of time without regard to direction.
16
A naval warship accelerates from rest at 0.5 m/s^2 for 40 seconds. What distance does it cover during this period?
Explanation: s = vi*t + 0.5*a*t^2 = 0 + 0.5 * 0.5 * (40^2) = 0.25 * 1600 = 400 meters.
17
At the peak of a projectile's trajectory, which component of its velocity becomes zero?
Explanation: At maximum height, the vertical velocity component vy is momentarily zero, while the horizontal velocity vx remains constant (ignoring air resistance).
18
What is the slope of a displacement-time graph equal to?
Explanation: The slope of a displacement-time graph (ds/dt) represents instantaneous velocity.
19
A depth charge is dropped from rest into water from a helicopter hovering 44.1 m above the sea surface. How long does it take to hit the water? (g = 9.8 m/s^2)
Explanation: h = 0.5*g*t^2 => 44.1 = 0.5 * 9.8 * t^2 = 4.9 * t^2 => t^2 = 9 => t = 3 seconds.
20
When a body moves along a circular path at constant speed, what is the direction of its acceleration?
Explanation: In uniform circular motion, centripetal acceleration always points radially inward toward the center of curvature.
21
Which law of Newton provides the quantitative definition and formula for Force (F = ma)?
Explanation: Newton's Second Law states that force is directly proportional to the rate of change of momentum (F = dp/dt = ma).
22
The property of a physical body to resist changes in its state of rest or uniform motion is called:
Explanation: Inertia is the inherent tendency of mass to resist any change in velocity or direction, directly proportional to its mass.
23
When a naval cannon fires a shell forward, why does the cannon recoil backwards?
Explanation: By the law of conservation of momentum, total momentum before firing is zero, so forward momentum of the shell equals recoil momentum of the cannon.
24
What is the relationship between the coefficient of static friction (mu_s) and the coefficient of kinetic friction (mu_k)?
Explanation: Static friction is always greater than kinetic friction because more force is required to break microscopic inter-molecular bonds than to maintain slip.
25
A naval cargo crate of mass 50 kg rests on a steel deck. If the coefficient of static friction is 0.4, what horizontal force is needed to start motion? (g = 9.8 m/s^2)
Explanation: Limiting friction Fs = mu_s * N = mu_s * m * g = 0.4 * 50 * 9.8 = 196 N.
26
A gun of mass 4 kg fires a bullet of mass 0.02 kg with a muzzle velocity of 400 m/s. What is the recoil velocity of the gun?
Explanation: M*V + m*v = 0 => 4 * V + (0.02 * 400) = 0 => 4*V + 8 = 0 => V = -8/4 = -2.0 m/s.
27
In an isolated physical system, which quantity is always conserved during an inelastic collision?
Explanation: Linear momentum is conserved in all collisions (elastic or inelastic) in an isolated system, while kinetic energy is conserved only in elastic collisions.
28
What force acts on a marine recruit standing in an elevator accelerating downwards at acceleration 'a'?
Explanation: The apparent weight in a downward accelerating elevator is R = m*(g - a). When a = g, apparent weight is zero (weightlessness).
29
Why are rolling bearings and lubrication grease widely used on ship propeller shafts?
Explanation: Rolling friction is significantly lower than sliding friction, minimizing energy loss and wear on rotating shafts.
30
The product of force and time during an instantaneous collision is known as:
Explanation: Impulse J = F * delta_t = delta_p, representing the total change in linear momentum delivered by a force.
31
When a naval tugboat applies a force of 10,000 N to pull a barge at an angle of 60 degrees to the displacement of 50 meters, what is the work done?
Explanation: W = F * d * cos(60 deg) = 10,000 * 50 * 0.5 = 250,000 Joules (or 250 kJ).
32
If the velocity of a naval torpedo is tripled, by what factor does its kinetic energy increase?
Explanation: Kinetic energy KE = 0.5 * m * v^2. If velocity is tripled (3v), KE becomes proportional to (3)^2 = 9 times.
33
How many watts are equivalent to one commercial unit of mechanical horsepower (hp)?
Explanation: One standard imperial horsepower (hp) is defined as approximately 746 Watts.
34
A crane on a naval dock lifts a 2,000 kg supply container through a vertical height of 15 meters in 10 seconds. What is the power consumed? (g = 9.8 m/s^2)
Explanation: Work = m*g*h = 2000 * 9.8 * 15 = 294,000 J. Power = W / t = 294,000 / 10 = 29,400 W = 29.4 kW.
35
What is the work done by the centripetal force on an object undergoing uniform circular motion?
Explanation: Centripetal force is always directed perpendicular to the displacement vector (cos 90 deg = 0), so work done is zero.
36
One kilowatt-hour (kWh) of electrical energy equals how many Joules?
Explanation: 1 kWh = 1000 W * 3600 s = 3,600,000 J = 3.6 x 10^6 Joules.
37
Which of the following is a non-conservative force in mechanical systems?
Explanation: Friction is a non-conservative force because work done against it depends on the path taken and cannot be fully recovered.
38
The escape velocity from Earth's gravitational field is approximately equal to:
Explanation: v_esc = sqrt(2 * g * R_earth) approx sqrt(2 * 9.8 * 6.4x10^6) approx 11.2 km/s.
39
If a marine engine delivers an output work of 600 J while consuming 800 J of thermal energy, what is its efficiency?
Explanation: Efficiency = (Output / Input) * 100 = (600 / 800) * 100 = 75%.
40
What type of energy is stored in the coiled spring of a marine chronometer or depth gauge?
Explanation: Compressing or stretching an elastic spring stores elastic potential energy equal to 0.5 * k * x^2.
41
What provides the necessary centripetal force to keep the Moon in orbit around Earth?
Explanation: The mutual gravitational pull between the Earth and Moon acts as the centripetal force sustaining orbital motion.
42
How does the value of acceleration due to gravity (g) vary as one moves from the Earth's equator to the poles?
Explanation: Because Earth is slightly flattened at the poles (smaller radius R) and rotational centrifugal reduction is zero at the poles, 'g' increases from equator to poles.
43
What is the orbital time period of a geostationary satellite used in naval communication networks?
Explanation: A geostationary satellite orbits Earth in 24 hours (1 sidereal day) in the equatorial plane, remaining fixed above one spot on Earth.
44
If the distance between two naval vessels is doubled, how does the gravitational force between them change?
Explanation: According to Newton's law of gravitation, F is inversely proportional to r^2. Doubling r reduces F to 1/(2^2) = 1/4th.
45
What is the angular speed (omega) of the second hand of a mechanical ship watch?
Explanation: The second hand completes 2*pi radians in 60 seconds. omega = 2*pi / 60 = pi / 30 rad/s.
46
At what point inside the Earth would the value of gravitational acceleration 'g' become exactly zero?
Explanation: At the geometric center of Earth, mass attracts equally in all directions, canceling out net gravitational force, making g = 0.
47
Why are naval gun barrels rifled with helical spiral grooves?
Explanation: Helical rifling imparts angular momentum to the projectile, giving gyroscopic stability to prevent tumbling in flight.
48
What is the critical speed required for an artificial satellite to orbit close to Earth's surface?
Explanation: First cosmic velocity (orbital speed near Earth) v = sqrt(g * R) approx sqrt(9.8 * 6.4x10^6) approx 7.9 km/s.
49
What happens to the weight of an astronaut inside an orbiting naval reconnaissance satellite?
Explanation: The satellite and astronaut are in free fall together, causing a sensation of weightlessness (apparent weight is zero), though gravity is still active.
50
The rotational kinetic energy of a spinning naval turbine wheel of moment of inertia 'I' and angular velocity 'omega' is given by:
Explanation: Rotational kinetic energy is analogous to translational KE (0.5 * m * v^2) and is given by KE_rot = 0.5 * I * omega^2.
51
Which fundamental principle explains why a heavy steel warship floats while a solid iron ball sinks?
Explanation: Archimedes' principle states that buoyant force equals the weight of displaced liquid. A hollow ship hull displaces an enormous volume of water whose weight exceeds the ship's weight.
52
How does a submarine regulate its diving depth and surfacing in seawater?
Explanation: Submarines adjust their average density: flooding ballast tanks with sea water increases weight to submerge; pumping compressed air expels water to surface.
53
Hydrostatic pressure at a depth 'h' below the surface of an ocean is given by which formula?
Explanation: Fluid pressure at depth h is P = rho * g * h, where rho is seawater density and g is gravitational acceleration.
54
Why does a loaded ship sink slightly deeper in fresh river water than in open sea water?
Explanation: Sea water is denser (approx 1025 kg/m^3) than fresh water (1000 kg/m^3), providing greater upthrust per unit volume displaced.
55
Which law states that pressure applied to an enclosed fluid is transmitted undiminished in all directions?
Explanation: Pascal's law states that pressure applied to an enclosed incompressibe fluid is transmitted equally to all parts of the fluid and container walls.
56
According to Bernoulli's principle, what happens to fluid pressure when its speed increases in a streamline flow?
Explanation: Bernoulli's theorem states P + 0.5*rho*v^2 + rho*g*h = constant. An increase in velocity v results in a corresponding drop in static pressure P.
57
The instrument specifically used to measure the specific gravity and salinity density of marine battery electrolyte is:
Explanation: A hydrometer is a floating glass device calibrated to measure the specific gravity (relative density) of liquids based on floatation.
58
What is the standard atmospheric pressure at sea level in Pascals (N/m^2)?
Explanation: 1 standard atmosphere (1 atm) = 760 mmHg = 101,325 Pa approx 1.013 x 10^5 Pa (or 1.013 bar).
59
The spherical shape of rain drops falling on a ship deck is primarily caused by:
Explanation: Surface tension minimizes surface area for a given volume, and a sphere has the least surface area per volume.
60
What term describes the constant maximum downward speed achieved by a sinking object when drag force equals gravitational weight?
Explanation: Terminal velocity is reached when fluid drag and buoyancy balance gravitational pull, resulting in zero net acceleration and constant falling speed.
61
What is absolute zero temperature in degrees Celsius?
Explanation: Absolute zero (0 Kelvin) is the theoretical lowest temperature where molecular motion ceases, corresponding to -273.15 °C.
62
Which mode of heat transfer can take place across a complete vacuum from the Sun to the Earth?
Explanation: Thermal radiation propagates via electromagnetic waves and requires no physical medium, allowing heat transfer across empty space.
63
Why does water expand when cooled between 4 °C and 0 °C?
Explanation: Water has maximum density at 4 °C; cooling below 4 °C forms open hexagonal hydrogen-bonded ice lattices, causing expansion.
64
The amount of heat required to raise the temperature of 1 kg of a substance by 1 Kelvin is called:
Explanation: Specific heat capacity c = Q / (m * delta_T), measuring thermal energy required to change unit mass temperature by 1 K.
65
According to the First Law of Thermodynamics, which physical quantity is conserved?
Explanation: The First Law of Thermodynamics (delta_Q = delta_U + delta_W) is an expression of the principle of conservation of energy.
66
In which thermodynamic process does the volume of the working gas remain strictly constant?
Explanation: An isochoric (or isometric) process occurs at constant volume (dV = 0), so work done W = P*dV is zero.
67
What is the maximum theoretical efficiency of a Carnot heat engine operating between temperatures T_hot and T_cold?
Explanation: Carnot efficiency eta = 1 - (T_C / T_H) where temperatures must be expressed in absolute Kelvin.
68
Why do marine sea breezes blow from ocean toward land during hot daylight hours?
Explanation: Water has very high specific heat capacity and heats up slowly; land heats faster, creating low pressure over land which draws in cooler sea air.
69
What happens to the internal energy of an ideal gas during an isothermal expansion?
Explanation: Internal energy of an ideal gas depends solely on temperature (U = f(T)). At constant temperature (isothermal), delta_U = 0.
70
The heat required to change a solid into liquid state without any temperature change is known as:
Explanation: Latent heat of fusion is the energy absorbed per unit mass during phase transition from solid to liquid at its melting point.
71
What type of wave is an acoustic sound wave traveling through seawater?
Explanation: Sound in water propagates as longitudinal mechanical compression and rarefaction waves, requiring a material medium.
72
How does the speed of sound in seawater compare to the speed of sound in air?
Explanation: Speed of sound in air is approx 340 m/s, whereas in seawater it is approx 1500 m/s (over 4.4 times faster) due to higher bulk modulus.
73
A naval frigate sends a SONAR acoustic pulse to the seabed and receives the echo after 4 seconds. If sound speed in seawater is 1500 m/s, what is ocean depth?
Explanation: Distance = (v * t) / 2 = (1500 * 4) / 2 = 6000 / 2 = 3000 meters.
74
What physical acronym does the naval underwater detection technology 'SONAR' stand for?
Explanation: SONAR stands for Sound Navigation and Ranging, utilizing acoustic propagation to detect and navigate underwater.
75
The apparent change in frequency of sound heard when a submarine and target vessel move relative to each other is known as:
Explanation: The Doppler Effect describes the observed shift in frequency or wavelength when source and observer move relative to each other.
76
What is the audible frequency range of acoustic waves for normal human ears?
Explanation: Normal human hearing spans frequencies between 20 Hz (infrasonic threshold) and 20 kHz (ultrasonic threshold).
77
Sound frequencies higher than 20,000 Hz used in naval depth sounders and medical imaging are termed:
Explanation: Frequencies above 20,000 Hz are ultrasonic waves, possessing high penetration and short wavelength suitable for imaging.
78
What happens when an external periodic force vibrates at a frequency exactly equal to the natural frequency of a system?
Explanation: Resonance occurs when driving frequency matches natural frequency, causing oscillations with drastically increased amplitude.
79
What is the fundamental wave speed formula relating speed (v), frequency (f), and wavelength (lambda)?
Explanation: Wave speed is the product of frequency and wavelength: v = f * lambda.
80
To produce a distinct human echo in air, what is the minimum distance required from the reflecting obstacle? (Speed of sound = 340 m/s)
Explanation: Human persistence of hearing is 0.1 s. Distance = (v * t) / 2 = (340 * 0.1) / 2 = 34 / 2 = 17 meters.
81
What optical principle allows a submarine periscope to view surface objects using two right-angled prisms?
Explanation: Periscopes use 45-45-90 degree totally reflecting glass prisms (critical angle 42 deg) where light reflects internally at 90 deg without silvering.
82
What condition is necessary for Total Internal Reflection (TIR) to occur?
Explanation: TIR requires light to travel from an optically denser to rarer medium and the angle of incidence must exceed the critical angle.
83
Modern naval fiber-optic communication cables transmit gigabits of signals based on:
Explanation: Optical fibers rely on repeated total internal reflection within a higher refractive index glass core clad by lower index cladding.
84
What is the speed of light in a vacuum in SI units?
Explanation: The speed of light in vacuum is defined as c approx 2.998 x 10^8 m/s approx 3.0 x 10^8 m/s.
85
A light ray travels from air (n = 1.0) into water (n = 1.33). What happens to its frequency, wavelength, and speed?
Explanation: Frequency is a characteristic of the source and remains constant upon refraction. Speed decreases (v = c/n) and wavelength shortens (lambda = lambda_0/n).
86
Which type of lens is used to correct myopia (short-sightedness) in naval medical examinations?
Explanation: Myopia occurs when images form in front of the retina. A diverging (concave) lens diverges incoming rays to focus sharply on the retina.
87
What is the power of a convex lens having a focal length of +50 cm?
Explanation: Power P = 1 / f(in meters). f = 50 cm = 0.5 m => P = 1 / 0.5 = +2.0 Diopters.
88
Splitting of white light into its seven constituent spectral colors when passing through a prism is called:
Explanation: Dispersion is the separation of composite white light into spectrum colors because different wavelengths experience different refractive indices.
89
Which electromagnetic wave possesses the shortest wavelength and highest frequency in the spectrum?
Explanation: Gamma rays have the highest photon energy and frequencies (> 10^19 Hz) with sub-picometer wavelengths.
90
What phenomenon proves that light waves are transverse in nature rather than longitudinal?
Explanation: Only transverse waves (oscillating perpendicular to propagation) can be polarized. Longitudinal waves cannot be polarized.
91
According to Ohm's Law, what is the relation between current (I), voltage (V), and resistance (R) at constant temperature?
Explanation: Ohm's law states that current through a conductor is proportional to potential difference: V = I * R.
92
Two resistors of 6 ohms and 3 ohms are connected in parallel in a naval battery circuit. What is the equivalent resistance?
Explanation: 1/R_eq = 1/6 + 1/3 = 3/6 = 1/2 => R_eq = 2.0 ohms.
93
Which law states that an induced electromotive force (EMF) always opposes the change in magnetic flux that creates it?
Explanation: Lenz's Law is a manifestation of conservation of energy: EMF = -dPhi/dt, where the negative sign indicates opposition to flux change.
94
What device is used to step up or step down alternating voltage in marine electrical distribution panels?
Explanation: A transformer steps AC voltages up or down based on mutual electromagnetic induction between primary and secondary coils.
95
What is the SI unit of electric capacitance?
Explanation: Capacitance C = Q / V is measured in Farads (F), named after Michael Faraday.
96
What is the magnetic force on a charge 'q' moving with velocity 'v' parallel to a magnetic field 'B'?
Explanation: Lorentz magnetic force F = q * v * B * sin(theta). When moving parallel, theta = 0 deg, so sin(0) = 0 and force is zero.
97
Which type of radioactive decay emission consists of helium nuclei containing two protons and two neutrons?
Explanation: An alpha particle is a helium-4 nucleus (2 protons, 2 neutrons) carrying a +2e charge.
98
If the half-life of a radioactive isotope is 8 days, what fraction of the original sample remains after 24 days?
Explanation: Number of half-lives n = 24 / 8 = 3. Remaining fraction = (1/2)^3 = 1/8.
99
What nuclear reaction powers nuclear-propelled naval submarines and aircraft carriers?
Explanation: Naval nuclear reactors generate propulsion steam via controlled chain fission of enriched Uranium-235 in a pressurized water reactor.
100
What is Einstein's mass-energy equivalence equation?
Explanation: Albert Einstein's famous 1905 equation states E = m * c^2, showing that mass and energy are inter-convertible.
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