I85PREP
⌘ K
Bihar Polytechnic study materials
Bihar Polytechnic study resources

Bihar Polytechnic practice questions

One question at a time. Build your Bihar Polytechnic understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Physics

A body moves along a straight line with uniform acceleration. Which quantity remains constant during the motion?

  1. Distance travelled per second
  2. Velocity of the body
  3. Rate of change of velocity Correct answer.
  4. Magnitude of displacement

Explanation

Uniform acceleration means the velocity changes by equal amounts in equal time intervals, so the rate of change of velocity (acceleration) is fixed. Velocity itself keeps changing, and distance per second equals speed, which also changes. Only the acceleration stays constant.

Question 2Physics

A stone is dropped from rest and falls freely under gravity. Taking g = 10 m/s², how far does it fall in the first 3 seconds?

  1. 15 m
  2. 30 m
  3. 45 m Correct answer.
  4. 90 m

Explanation

Using s = ut + ½at² with u = 0, a = 10 m/s² and t = 3 s gives s = ½ × 10 × 9 = 45 m. The initial velocity contributes nothing because the stone starts from rest.

Question 3Physics

A projectile is launched at an angle to the horizontal in the absence of air resistance. At the highest point of its path, what is true of its acceleration?

  1. It is g directed vertically upward
  2. It equals g directed vertically downward Correct answer.
  3. It equals g directed along the velocity
  4. It is zero because vertical velocity vanishes

Explanation

Throughout the flight the only force is gravity, so the acceleration is g directed downward at every instant, including the top. At the top the vertical velocity is momentarily zero, but the acceleration is not. The horizontal velocity is unchanged, so the acceleration is not along the velocity.

Question 4Physics

Two forces of 6 N and 8 N act at a single point at right angles to each other. What is the magnitude of their resultant?

  1. 10 N Correct answer.
  2. 2 N
  3. 14 N
  4. 7 N

Explanation

For perpendicular forces the resultant is found from the Pythagorean relation R = √(6² + 8²) = √100 = 10 N. Simple addition would apply only if the forces were parallel and in the same direction.

Question 5Physics

A body of mass 5 kg experiences a net force of 20 N. What is its acceleration?

  1. 0.25 m/s²
  2. 25 m/s²
  3. 100 m/s²
  4. 4 m/s² Correct answer.

Explanation

Newton's second law gives a = F/m = 20/5 = 4 m/s². The acceleration is directly proportional to the net force and inversely proportional to the mass.

Question 6Physics

A book rests on a horizontal table. Which pair of forces forms an action–reaction pair according to Newton's third law?

  1. Earth pulls the book down; the book pulls Earth up Correct answer.
  2. The book presses the table down; the table supports the book up
  3. Earth pulls the book down; the table pushes the book up
  4. The book's weight acts down; friction acts along the table

Explanation

Action–reaction pairs act on different bodies and are of the same type. The gravitational pull of Earth on the book and the book's gravitational pull on Earth are equal, opposite and act on different bodies. The normal force and weight balance the book but act on the same body, so they are not a third-law pair.

Question 7Physics

A block slides down a rough inclined plane at constant velocity. What is the net force on the block?

  1. Zero Correct answer.
  2. Equal to its weight
  3. Directed up the plane
  4. Directed down the plane

Explanation

Constant velocity means zero acceleration, so by Newton's first law the vector sum of all forces must be zero. The component of weight down the plane is exactly balanced by friction up the plane. A non-zero net force would produce acceleration.

Question 8Physics

The work done by a force on a body is zero when the angle between the force and the displacement is

  1. 0°
  2. 90° Correct answer.
  3. 180°
  4. 45°

Explanation

Work is W = F s cos θ, and cos 90° = 0, so the work vanishes when the force is perpendicular to the displacement. This is why the centripetal force does no work on a body in uniform circular motion.

Question 9Physics

A pump raises 200 kg of water through a height of 10 m in 5 s. Taking g = 10 m/s², what is the useful power output?

  1. 20000 W
  2. 2000 W
  3. 400 W
  4. 4000 W Correct answer.

Explanation

The work done against gravity is mgh = 200 × 10 × 10 = 20 000 J, and power is work divided by time: 20 000/5 = 4000 W. Power measures the rate of doing work, not the total work.

Question 10Physics

A moving body collides head-on with an identical stationary body and they stick together. The collision is

  1. Inelastic, with momentum not conserved
  2. Elastic, with momentum lost
  3. Elastic, with kinetic energy conserved
  4. Perfectly inelastic, with kinetic energy lost Correct answer.

Explanation

When bodies stick together after impact, the collision is perfectly inelastic and the maximum possible kinetic energy is converted into other forms. Momentum is still conserved in every collision where external impulses are negligible. Kinetic energy is not conserved in an inelastic collision.

Question 11Physics

The moment of inertia of a body about an axis depends on

  1. Only the angular velocity of the body
  2. The distribution of mass about that axis Correct answer.
  3. Only the total mass of the body
  4. Only the torque applied to the body

Explanation

Moment of inertia is I = Σmr², so both the mass and how far it lies from the axis matter. Two bodies of equal mass can have very different moments of inertia depending on their shape. It is a property of the body and axis, not of its motion.

Question 12Physics

A satellite orbits Earth in a circular path. If the radius of the orbit is increased, the orbital speed

  1. Increases
  2. Becomes zero
  3. Remains the same
  4. Decreases Correct answer.

Explanation

Gravitational attraction provides the centripetal force, so GMm/r² = mv²/r, giving v = √(GM/r). The orbital speed therefore falls as the radius increases. A larger orbit is slower but has a longer period.

Question 13Physics

According to Kepler's second law, the line joining a planet to the Sun sweeps out equal areas in equal times. This implies that the planet's

  1. Angular momentum about the Sun is constant Correct answer.
  2. Linear speed is constant throughout the orbit
  3. Distance from the Sun is constant
  4. Total energy changes along the orbit

Explanation

Equal areas in equal times is equivalent to constant areal velocity, which means the angular momentum about the Sun is conserved. As a result the planet moves faster when nearer the Sun and slower when farther away. Its distance and speed both vary around the orbit.

Question 14Physics

A body floats in equilibrium with part of its volume above the surface of a liquid. Which statement about the forces on it is correct?

  1. The buoyant force equals the weight of the whole body's volume of liquid
  2. The buoyant force equals the weight of the body Correct answer.
  3. The buoyant force exceeds the weight of the body
  4. The weight of the body exceeds the buoyant force

Explanation

For a floating body at rest, the upward buoyant force balances its weight. By Archimedes' principle the buoyant force equals the weight of the liquid displaced, which is the submerged volume only. The displaced liquid weighs the same as the whole floating body.

Question 15Physics

Water flows steadily through a horizontal pipe whose cross-sectional area decreases. In the narrower section, the speed of the water

  1. Remains unchanged in both respects
  2. Increases and the pressure decreases Correct answer.
  3. Increases and the pressure increases
  4. Decreases and the pressure increases

Explanation

The equation of continuity, A₁v₁ = A₂v₂, shows that the speed rises where the area falls. Bernoulli's principle then requires the pressure to drop in the faster-moving section, since the sum of pressure and kinetic energy terms stays constant along a horizontal streamline.

Question 16Physics

The surface tension of a liquid is best described as the

  1. Force per unit area acting normal to the surface
  2. Energy required to heat the liquid
  3. Pressure exerted by the liquid on its container
  4. Force per unit length acting along the liquid surface Correct answer.

Explanation

Surface tension is the force per unit length along a line drawn on the liquid surface, and it also equals the surface energy per unit area. It arises because molecules at the surface have higher potential energy than those in the bulk. It is not a pressure or a thermal quantity.

Question 17Physics

A steel rod of length 1 m is heated through 50 °C. If its coefficient of linear expansion is 1.2 × 10⁻⁵ per °C, what is its increase in length?

  1. 6.0 × 10⁻³ m
  2. 2.4 × 10⁻⁴ m
  3. 1.2 × 10⁻³ m
  4. 6.0 × 10⁻⁴ m Correct answer.

Explanation

Linear expansion is ΔL = L α ΔT = 1 × 1.2 × 10⁻⁵ × 50 = 6.0 × 10⁻⁴ m. The change is proportional to the original length, the coefficient and the temperature rise.

Question 18Physics

In an isothermal process for an ideal gas, the change in internal energy is

  1. Equal to the heat supplied
  2. Negative, because volume changes
  3. Equal to the work done by the gas
  4. Zero, because temperature stays constant Correct answer.

Explanation

The internal energy of an ideal gas depends only on its temperature, so at constant temperature the internal energy does not change. By the first law, all heat supplied then appears as work done by the gas. Internal energy does not depend on volume for an ideal gas.

Question 19Physics

Two identical waves travelling in opposite directions in the same medium superpose. The resulting pattern is

  1. A travelling wave of double amplitude
  2. A wave of zero amplitude everywhere
  3. A standing wave with fixed nodes and antinodes Correct answer.
  4. A wave with frequency doubled at every point

Explanation

Superposition of equal waves moving in opposite directions produces a standing wave. Points of permanently zero displacement are nodes and points of maximum displacement are antinodes. The pattern does not translate through the medium.

Question 20Physics

A sound source of frequency 500 Hz moves toward a stationary observer. The frequency heard by the observer will be

  1. Independent of the source's speed
  2. Exactly 500 Hz
  3. Greater than 500 Hz Correct answer.
  4. Less than 500 Hz

Explanation

When the source approaches, successive wavefronts are compressed into a shorter distance, so the observed wavelength falls and the heard frequency rises. This is the Doppler effect. The shift grows with the speed of approach.

Question 21Physics

Light passes from air into glass of refractive index 1.5. Compared with air, inside the glass the light has

  1. A smaller speed and a longer wavelength
  2. A larger speed and a shorter wavelength
  3. A smaller speed and a shorter wavelength Correct answer.
  4. The same speed and the same wavelength

Explanation

The refractive index is n = c/v, so light travels slower in glass by a factor of 1.5. Its frequency is fixed by the source, so the wavelength shortens in the same ratio. Frequency, not wavelength, stays constant across the boundary.

Question 22Physics

An object is placed between the pole and the principal focus of a concave mirror. The image formed is

  1. Virtual, erect and magnified Correct answer.
  2. Real, inverted and magnified
  3. Virtual, erect and diminished
  4. Real, inverted and diminished

Explanation

For a concave mirror, an object inside the focal length gives a virtual, erect and enlarged image behind the mirror. This is the arrangement used in a shaving mirror. Real inverted images appear only when the object lies beyond the focus.

Question 23Physics

Two resistors of 4 Ω and 6 Ω are connected in parallel. What is the equivalent resistance?

  1. 2.4 Ω Correct answer.
  2. 1.5 Ω
  3. 5 Ω
  4. 10 Ω

Explanation

For parallel resistors, 1/R = 1/4 + 1/6 = 5/12, so R = 12/5 = 2.4 Ω. The equivalent resistance of a parallel combination is always less than the smallest individual resistance.

Question 24Physics

A wire of resistance R is stretched uniformly so that its length is doubled. Its new resistance is

  1. 2R
  2. R/4
  3. 4R Correct answer.
  4. R/2

Explanation

Stretching keeps the volume constant, so doubling the length halves the cross-sectional area. Since R = ρL/A, doubling L and halving A multiplies the resistance by four. The resistivity itself does not change.

Question 25Physics

A charged particle enters a uniform magnetic field moving parallel to the field lines. The magnetic force on the particle is

  1. Zero Correct answer.
  2. Maximum and perpendicular to the velocity
  3. Along the velocity
  4. Opposite to the velocity

Explanation

The magnetic force is F = qvB sin θ, where θ is the angle between velocity and field. For parallel motion sin θ = 0, so no magnetic force acts. The force is greatest when the velocity is perpendicular to the field.

Question 26Physics

A particle moves in a straight line with constant acceleration. Which graph of displacement versus time is a parabola?

  1. Displacement-time graph for zero acceleration
  2. Displacement-time graph for uniform acceleration Correct answer.
  3. Displacement-time graph for uniform velocity
  4. Displacement-time graph for negative acceleration

Explanation

For constant acceleration, displacement is given by s = ut + ½at², which is a quadratic equation in time, so the displacement-time graph is a parabola. Uniform velocity gives a straight line, and zero acceleration also gives a straight line.

Question 27Physics

A ball is thrown vertically upward with a speed of 20 m/s. Taking g = 10 m/s², what is the maximum height reached?

  1. 30 m
  2. 20 m Correct answer.
  3. 40 m
  4. 10 m

Explanation

At maximum height the final velocity is zero. Using v² = u² - 2gh, we get 0 = (20)² - 2(10)h, so h = 400/20 = 20 m.

Question 28Physics

A force of 10 N acts on a body of mass 2 kg for 3 s. What is the change in momentum of the body?

  1. 6.7 kg m/s
  2. 30 kg m/s Correct answer.
  3. 60 kg m/s
  4. 15 kg m/s

Explanation

Impulse equals change in momentum: F × t = 10 N × 3 s = 30 kg m/s. This follows directly from Newton's second law in impulse form.

Question 29Physics

A wheel starting from rest attains an angular velocity of 20 rad/s in 5 s. What is its angular acceleration?

  1. 5 rad/s²
  2. 4 rad/s² Correct answer.
  3. 100 rad/s²
  4. 2 rad/s²

Explanation

Angular acceleration α = (ω - ω₀)/t = (20 - 0)/5 = 4 rad/s². This is the rotational analogue of linear acceleration.

Question 30Physics

The acceleration due to gravity at the surface of a planet is g. At a height equal to the radius of the planet above its surface, the acceleration due to gravity is

  1. g/8
  2. g/2
  3. g/16
  4. g/4 Correct answer.

Explanation

Acceleration due to gravity is inversely proportional to the square of the distance from the centre. At height R above the surface, the distance from the centre is 2R, so g' = g (R/(2R))² = g/4.

Question 31Physics

A body of mass 2 kg is moving with a velocity of 3 m/s. What is its kinetic energy?

  1. 6 J
  2. 9 J Correct answer.
  3. 12 J
  4. 18 J

Explanation

Kinetic energy is given by KE = ½mv². Substituting m = 2 kg and v = 3 m/s gives KE = ½ × 2 × 3² = 9 J.

Question 32Physics

In a perfectly elastic collision between two bodies, which quantity is conserved?

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

Explanation

In any collision without external forces, momentum is conserved. In a perfectly elastic collision, kinetic energy is also conserved because no energy is lost to deformation or heat.

Question 33Physics

A solid sphere and a solid cylinder of the same mass and radius roll down an inclined plane without slipping from the same height. Which reaches the bottom first?

  1. It depends on the angle of inclination
  2. Both reach at the same time
  3. The solid sphere Correct answer.
  4. The solid cylinder

Explanation

The acceleration of a rolling body is a = g sinθ / (1 + I/(MR²)). For a solid sphere, I = (2/5)MR², giving a = (5/7)g sinθ; for a cylinder, I = (1/2)MR², giving a = (2/3)g sinθ. Since 5/7 > 2/3, the sphere accelerates more and reaches the bottom first.

Question 34Physics

A body floats in a liquid with 1/4 of its volume above the liquid surface. What is the ratio of the density of the body to the density of the liquid?

  1. 4:1
  2. 1:3
  3. 1:4
  4. 3:4 Correct answer.

Explanation

For a floating body, the fraction of volume submerged equals the ratio of densities. Since 1/4 is above, 3/4 is submerged, so density of body / density of liquid = 3/4.

Question 35Physics

The terminal velocity of a small sphere falling through a viscous liquid is proportional to

  1. the radius of the sphere
  2. the inverse of the radius
  3. the cube of the radius
  4. the square of the radius Correct answer.

Explanation

By Stokes' law, the viscous force is 6πηrv, and at terminal velocity this balances the net downward force (weight minus buoyancy), which is proportional to r³. Equating gives v ∝ r², so terminal velocity is proportional to the square of the radius.

Question 36Physics

The coefficient of linear expansion of a metal is 2 × 10⁻⁵ per °C. What is the coefficient of superficial expansion?

  1. 6 × 10⁻⁵ per °C
  2. 4 × 10⁻⁵ per °C Correct answer.
  3. 2 × 10⁻⁵ per °C
  4. 8 × 10⁻⁵ per °C

Explanation

The coefficient of superficial expansion β is approximately twice the coefficient of linear expansion α: β = 2α. Thus β = 2 × 2 × 10⁻⁵ = 4 × 10⁻⁵ per °C.

Question 37Physics

In an adiabatic process for an ideal gas, the relation between pressure and volume is

  1. PV^γ = constant Correct answer.
  2. P/V = constant
  3. P + V = constant
  4. PV = constant

Explanation

For an adiabatic process (no heat exchange), the ideal gas law combined with the first law gives PV^γ = constant, where γ is the ratio of specific heats. PV = constant applies to an isothermal process.

Question 38Physics

A Carnot engine operates between a source at 500 K and a sink at 300 K. What is its efficiency?

  1. 40% Correct answer.
  2. 20%
  3. 60%
  4. 80%

Explanation

The efficiency of a Carnot engine is η = 1 - T_sink/T_source = 1 - 300/500 = 1 - 0.6 = 0.4, or 40%.

Question 39Physics

A simple pendulum has a time period T on Earth. What will be its time period on the Moon, where acceleration due to gravity is about one-sixth of that on Earth?

  1. T/√6
  2. T/6
  3. √6 T Correct answer.
  4. 6T

Explanation

The time period of a simple pendulum is T = 2π√(L/g). If g becomes g/6, then the new period is 2π√(L/(g/6)) = √6 × 2π√(L/g) = √6 T.

Question 40Physics

A wave has a frequency of 50 Hz and a wavelength of 4 m. What is its speed?

  1. 54 m/s
  2. 0.08 m/s
  3. 12.5 m/s
  4. 200 m/s Correct answer.

Explanation

Wave speed is given by v = fλ. Substituting f = 50 Hz and λ = 4 m gives v = 50 × 4 = 200 m/s.

Question 41Physics

In a stationary wave pattern, the distance between two consecutive nodes is

  1. one wavelength
  2. twice the wavelength
  3. half a wavelength Correct answer.
  4. one quarter of a wavelength

Explanation

In a stationary wave, nodes occur at points of zero amplitude. Adjacent nodes are separated by half a wavelength, because the wave repeats every half wavelength in space for a standing wave.

Question 42Physics

A sound wave travels from air into water. Which property of the wave remains unchanged?

  1. Amplitude
  2. Speed
  3. Frequency Correct answer.
  4. Wavelength

Explanation

When a wave crosses a boundary between media, its frequency is determined by the source and remains constant. Speed and wavelength change because they depend on the medium.

Question 43Physics

An object is placed at the centre of curvature of a concave mirror. Where is the image formed?

  1. At infinity
  2. Between the pole and the focus
  3. At the focus
  4. At the centre of curvature Correct answer.

Explanation

For a concave mirror, when the object is at the centre of curvature, the image is also formed at the centre of curvature, real, inverted, and of the same size.

Question 44Physics

The critical angle for a certain glass-air interface is 30°. What is the refractive index of the glass?

  1. 2.0 Correct answer.
  2. 1.5
  3. 2.5
  4. 1.73

Explanation

The critical angle C is related to refractive index n by sin C = 1/n. For C = 30°, sin 30° = 0.5, so n = 1/0.5 = 2.0.

Question 45Physics

A convex lens of focal length 10 cm forms a real image at a distance of 20 cm from the lens. What is the object distance?

  1. 30 cm
  2. 15 cm
  3. 20 cm Correct answer.
  4. 10 cm

Explanation

Using the lens formula 1/f = 1/v - 1/u with f = 10 cm and v = 20 cm (real image, so v positive), we get 1/10 = 1/20 - 1/u, so 1/u = 1/20 - 1/10 = -1/20, giving u = -20 cm. The object distance is 20 cm.

Question 46Physics

Two point charges of +2 μC and +8 μC are placed 0.2 m apart in air. At what distance from the +2 μC charge is the electric field zero?

  1. 0.067 m Correct answer.
  2. 0.04 m
  3. 0.1 m
  4. 0.133 m

Explanation

The electric field is zero at a point between the charges where the fields cancel. Let x be the distance from the 2 μC charge. Then k(2)/x² = k(8)/(0.2 - x)². Solving gives (0.2 - x)/x = 2, so 0.2 - x = 2x, 3x = 0.2, x = 0.0667 m.

Question 47Physics

A 12 V battery is connected across a 4 Ω resistor. What is the power dissipated in the resistor?

  1. 3 W
  2. 36 W Correct answer.
  3. 144 W
  4. 48 W

Explanation

Power is given by P = V²/R. Substituting V = 12 V and R = 4 Ω gives P = 144/4 = 36 W.

Question 48Physics

A galvanometer of resistance 100 Ω gives a full-scale deflection for a current of 1 mA. How can it be converted into a voltmeter of range 10 V?

  1. By connecting a resistance of 100 Ω in series
  2. By connecting a resistance of 100 Ω in parallel
  3. By connecting a resistance of 9900 Ω in parallel
  4. By connecting a resistance of 9900 Ω in series Correct answer.

Explanation

To convert a galvanometer into a voltmeter, a high resistance is connected in series. The required series resistance R = V/I_g - G = 10/(1×10⁻³) - 100 = 10000 - 100 = 9900 Ω.

Question 49Physics

A charged particle moves in a circular path in a uniform magnetic field. If its speed is doubled while the field remains the same, the radius of the path

  1. becomes four times
  2. is doubled Correct answer.
  3. remains the same
  4. is halved

Explanation

The radius of a charged particle in a magnetic field is r = mv/(qB). If speed v is doubled while m, q, and B remain constant, the radius r also doubles.

Question 50Physics

The peak value of an alternating current is 10 A. What is its root mean square value?

  1. 5 A
  2. 14.14 A
  3. 10 A
  4. 7.07 A Correct answer.

Explanation

For a sinusoidal alternating current, the rms value is I_peak/√2. Thus I_rms = 10/1.414 ≈ 7.07 A.