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Jharkhand Polytechnic (PECE) practice questions

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Question 1Physics

A body moves along a straight line with uniform acceleration. Starting from rest, it covers 100 m in 10 s. What is its acceleration?

  1. 10 m/s²
  2. 1 m/s²
  3. 5 m/s²
  4. 2 m/s² Correct answer.

Explanation

Using s = ut + ½at² with u = 0, we get 100 = ½·a·100, so a = 2 m/s². The displacement grows with the square of time when the body starts from rest, so the average speed over the interval is only 10 m/s while the final speed is 20 m/s.

Question 2Physics

Which physical quantity is a scalar?

  1. Velocity
  2. Work Correct answer.
  3. Acceleration
  4. Displacement

Explanation

Work is the scalar product of force and displacement, so it has magnitude but no direction and is described by a single number with units. Displacement, velocity and acceleration are all vectors because each requires a direction to be fully specified.

Question 3Physics

A force of 20 N acts on a body of mass 4 kg on a frictionless surface. What is the acceleration produced?

  1. 80 m/s²
  2. 0.2 m/s²
  3. 24 m/s²
  4. 5 m/s² Correct answer.

Explanation

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

Question 4Physics

The SI unit of the universal gravitational constant G is

  1. N m² kg⁻² Correct answer.
  2. N m² kg⁻¹
  3. N kg⁻²
  4. N m kg⁻²

Explanation

From F = G m₁m₂/r², rearranging gives G = F r²/(m₁m₂), so the unit is N m² kg⁻². The kilogram appears squared in the denominator because both masses contribute to the force.

Question 5Physics

A block of mass 2 kg rests on a horizontal surface with coefficient of static friction 0.4. Taking g = 10 m/s², what is the maximum static friction force?

  1. 8 N Correct answer.
  2. 20 N
  3. 4 N
  4. 10 N

Explanation

The limiting static friction equals μN, and on a horizontal surface N = mg = 2 × 10 = 20 N. Hence f = 0.4 × 20 = 8 N. Static friction can take any value up to this limit depending on the applied force.

Question 6Physics

A body of mass 5 kg is lifted vertically through 4 m at constant velocity. Taking g = 10 m/s², the work done against gravity is

  1. 200 J Correct answer.
  2. 2000 J
  3. 20 J
  4. 50 J

Explanation

At constant velocity the applied force equals the weight, mg = 50 N, and work is force times displacement, so W = 50 × 4 = 200 J. This work is stored as gravitational potential energy of the body.

Question 7Physics

Two bodies of masses m and 2m move with equal kinetic energies. What is the ratio of their momenta, p₁ : p₂?

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

Explanation

Since K = p²/2m, equal kinetic energies give p² ∝ m, so p ∝ √m. Thus p₁ : p₂ = √m : √(2m) = 1 : √2, which is the same as √2 : 1 when written the other way round.

Question 8Physics

A wheel starting from rest accelerates uniformly to 20 rad/s in 5 s. What is its angular acceleration?

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

Explanation

Angular acceleration is the change in angular velocity divided by time: α = (20 − 0)/5 = 4 rad/s². This mirrors the linear relation a = Δv/t for straight-line motion.

Question 9Physics

The moment of inertia of a solid sphere of mass M and radius R about a diameter is

  1. (2/5)MR² Correct answer.
  2. MR²
  3. (2/3)MR²
  4. (1/2)MR²

Explanation

For a uniform solid sphere rotating about a diameter, the moment of inertia is (2/5)MR². The factor 2/5 arises because mass is distributed throughout the volume rather than concentrated at the surface or at a fixed radius.

Question 10Physics

The escape velocity from the Earth's surface is independent of which of the following?

  1. Gravitational constant G
  2. Radius of the Earth
  3. Mass of the projected body Correct answer.
  4. Mass of the Earth

Explanation

Escape velocity is v = √(2GM/R), which contains only the mass and radius of the planet and the gravitational constant. The mass of the escaping body cancels out because the required kinetic energy and the gravitational pull both scale with it.

Question 11Physics

A simple pendulum has a time period of 2 s on Earth. What is its approximate time period on the Moon, where g is about one-sixth of that on Earth?

  1. About 0.82 s
  2. About 0.33 s
  3. About 2 s
  4. About 4.9 s Correct answer.

Explanation

The period of a simple pendulum is T = 2π√(L/g), so T ∝ 1/√g. Reducing g to one-sixth multiplies the period by √6 ≈ 2.45, giving 2 × 2.45 ≈ 4.9 s.

Question 12Physics

In simple harmonic motion, the acceleration of the particle is

  1. constant in magnitude and direction
  2. directly proportional to displacement and directed away from the mean position
  3. directly proportional to displacement and directed towards the mean position Correct answer.
  4. maximum at the mean position and zero at the extreme positions

Explanation

The defining relation of simple harmonic motion is a = −ω²x, so acceleration is proportional to displacement and always points back towards the equilibrium position. This restoring character is what keeps the motion oscillatory and bounded.

Question 13Physics

The speed of sound in air is approximately 340 m/s. What is the wavelength of a sound wave of frequency 170 Hz?

  1. 57800 m
  2. 0.5 m
  3. 5 m
  4. 2 m Correct answer.

Explanation

For any wave, speed equals frequency times wavelength, so λ = v/f = 340/170 = 2 m. Higher-frequency sound has a shorter wavelength in the same medium because the speed is fixed by the medium.

Question 14Physics

Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. How many beats are heard per second?

  1. 4 Correct answer.
  2. 8
  3. 2
  4. 516

Explanation

The beat frequency equals the difference between the two frequencies, so 260 − 256 = 4 beats per second. Beats arise from the periodic reinforcement and cancellation of two superposed waves of slightly different frequencies.

Question 15Physics

A wave travels from a rarer medium into a denser medium. Which quantity remains unchanged?

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

Explanation

Frequency is fixed by the source and does not change when a wave crosses a boundary between media. Speed and wavelength both change, because the speed is set by the properties of the medium and λ = v/f adjusts accordingly.

Question 16Physics

The temperature of a body is raised from 27 °C to 127 °C. What is the ratio of the root-mean-square speed of its gas molecules at the two temperatures?

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

Explanation

The rms speed is proportional to √T with T in kelvin, so the temperatures 300 K and 400 K give the ratio √300 : √400 = √3 : 2. Using Celsius values directly would give a meaningless ratio because the scale does not start at absolute zero.

Question 17Physics

In an isothermal process for an ideal gas, which statement is correct?

  1. The work done by the gas is zero
  2. No heat is exchanged with the surroundings
  3. The internal energy remains constant Correct answer.
  4. The pressure remains constant

Explanation

For an ideal gas the internal energy depends only on temperature, so at constant temperature it does not change. Any heat supplied is therefore converted entirely into work done by the gas, in line with the first law of thermodynamics.

Question 18Physics

The first law of thermodynamics, ΔQ = ΔU + ΔW, is a statement of

  1. conservation of momentum
  2. the second law of thermodynamics
  3. conservation of charge
  4. conservation of energy Correct answer.

Explanation

The first law states that heat supplied to a system is shared between a change in internal energy and work done by the system, which is conservation of energy applied to thermal processes. It does not by itself restrict the direction in which processes may proceed.

Question 19Physics

Two point charges are separated by a distance r in vacuum. If the distance is halved while the charges stay the same, the electrostatic force becomes

  1. one-quarter
  2. four times Correct answer.
  3. half
  4. twice

Explanation

Coulomb's law gives F ∝ 1/r², so halving the distance multiplies the force by 1/(1/2)² = 4. The inverse-square dependence makes the force grow rapidly as charges are brought closer together.

Question 20Physics

Three resistors of 2 Ω, 3 Ω and 6 Ω are connected in parallel. What is the equivalent resistance?

  1. 2 Ω
  2. 6 Ω
  3. 11 Ω
  4. 1 Ω Correct answer.

Explanation

For parallel resistors, 1/R = 1/2 + 1/3 + 1/6 = 1, so R = 1 Ω. The equivalent resistance in parallel is always smaller than the smallest individual resistance, which confirms the answer.

Question 21Physics

A wire of resistance R is stretched uniformly so that its length is doubled. What is its new resistance, assuming volume stays constant?

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

Explanation

Stretching to double length halves the cross-sectional area, since volume is conserved. Resistance depends on length divided by area, so doubling the length and halving the area together multiply R by four.

Question 22Physics

The magnetic force on a charge q moving with velocity v in a magnetic field B is maximum when the angle between v and B is

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

Explanation

The magnitude of the magnetic force is F = qvB sin θ, which reaches its maximum value of qvB when sin θ = 1, that is at 90°. When the velocity is parallel or antiparallel to the field, no magnetic force acts on the charge.

Question 23Physics

A step-down transformer has 1000 turns in the primary and 200 turns in the secondary. If the primary voltage is 220 V, the secondary voltage is approximately

  1. 44 V Correct answer.
  2. 11 V
  3. 1100 V
  4. 22 V

Explanation

For an ideal transformer, V₂/V₁ = N₂/N₁, so V₂ = 220 × 200/1000 = 44 V. A step-down transformer reduces voltage while increasing current, keeping the power roughly constant.

Question 24Physics

In a Young's double-slit experiment, the fringe width is 2 mm. If the distance between the slits is doubled while everything else is unchanged, the new fringe width is

  1. 4 mm
  2. 8 mm
  3. 1 mm Correct answer.
  4. 0.5 mm

Explanation

Fringe width is given by β = λD/d, so it is inversely proportional to the slit separation. Doubling d therefore halves the fringe width, giving 1 mm.

Question 25Physics

A convex lens of focal length 20 cm forms an image of an object placed 30 cm from the lens. Using the lens formula, the image distance is

  1. 10 cm
  2. 50 cm
  3. 60 cm Correct answer.
  4. 12 cm

Explanation

The lens formula gives 1/v − 1/u = 1/f, with u = −30 cm and f = +20 cm, so 1/v = 1/20 − 1/30 = 1/60 and v = 60 cm. The image is real and formed on the opposite side of the lens.

Question 26Physics

A car travels 30 m north and then 40 m east. What is the magnitude of its resultant displacement?

  1. 10 m
  2. 50 m Correct answer.
  3. 70 m
  4. 35 m

Explanation

The two displacements are perpendicular, so the resultant magnitude is found by the Pythagorean relation: √(30² + 40²) = √2500 = 50 m. Adding the distances gives total path length, not displacement.

Question 27Physics

A body moves with uniform acceleration. Which graph of velocity against time is a straight line?

  1. A curve passing through the origin with decreasing slope
  2. A horizontal line
  3. A straight line with constant slope Correct answer.
  4. A curve of increasing slope

Explanation

Acceleration is the rate of change of velocity, so on a velocity–time graph it equals the slope. Uniform acceleration therefore gives a straight line of constant slope, and the area under it gives the displacement.

Question 28Physics

A body is projected with speed u at an angle θ to the horizontal. Neglecting air resistance, what is the horizontal component of its velocity throughout the flight?

  1. u sin θ
  2. zero
  3. u tan θ
  4. u cos θ Correct answer.

Explanation

The initial velocity is resolved into a horizontal part u cos θ and a vertical part u sin θ. Since the only acceleration is vertical (gravity), the horizontal component stays constant at u cos θ during the flight.

Question 29Physics

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

  1. Equal to the component of weight along the plane
  2. Zero Correct answer.
  3. Equal to the force of friction
  4. Equal to the normal reaction

Explanation

Constant velocity means zero acceleration, so by Newton's first law the vector sum of all forces is zero. The component of weight down the plane is exactly balanced by friction, giving a zero resultant.

Question 30Physics

A force of 20 N acts on a body of mass 4 kg for 3 s, starting from rest. What is the change in momentum of the body?

  1. 15 kg m/s
  2. 60 kg m/s Correct answer.
  3. 20 kg m/s
  4. 240 kg m/s

Explanation

Impulse equals the change in momentum, and impulse is force multiplied by time. Thus Δp = 20 × 3 = 60 kg m/s, which is also the final momentum since the body started from rest.

Question 31Physics

A current of 2 A flows through a resistor of 15 Ω. What is the power dissipated in the resistor?

  1. 120 W
  2. 60 W Correct answer.
  3. 30 W
  4. 7.5 W

Explanation

Joule heating power in a resistor is P = I²R. Substituting gives P = (2)² × 15 = 4 × 15 = 60 W, which is the rate at which electrical energy becomes heat.

Question 32Physics

The dimensional formula of Planck's constant is the same as that of which quantity?

  1. Power
  2. Energy
  3. Angular momentum Correct answer.
  4. Force

Explanation

Planck's constant has dimensions of energy multiplied by time, that is, ML²T⁻¹. Angular momentum also has dimensions ML²T⁻¹, so the two quantities share the same dimensional formula.

Question 33Physics

A particle moves in a circle of radius 0.5 m with a constant speed of 4 m/s. What is its centripetal acceleration?

  1. 2 m/s²
  2. 8 m/s²
  3. 32 m/s² Correct answer.
  4. 16 m/s²

Explanation

Centripetal acceleration is v²/r for uniform circular motion. Here v²/r = 16/0.5 = 32 m/s², directed towards the centre of the circle.

Question 34Physics

A flywheel of moment of inertia 2 kg m² rotates at 10 rad/s. What is its rotational kinetic energy?

  1. 100 J Correct answer.
  2. 10 J
  3. 200 J
  4. 20 J

Explanation

Rotational kinetic energy is ½Iω². Substituting I = 2 kg m² and ω = 10 rad/s gives ½ × 2 × 100 = 100 J, the analogue of ½mv² for rotation.

Question 35Physics

A satellite orbits the Earth at a height small compared with the Earth's radius. If the orbital speed is v, what is the minimum launch speed needed from the surface to place it in that orbit, neglecting air resistance and Earth's rotation?

  1. 2v
  2. v
  3. √2 v Correct answer.
  4. v/√2

Explanation

The orbital speed satisfies v² = GM/R, while the escape speed satisfies v_e² = 2GM/R, so v_e = √2 v. Launching to a low orbit needs slightly less than escape speed but more than the orbital speed itself; the standard result for the required launch speed in this idealised case is √2 times the orbital speed.

Question 36Physics

A spring of force constant 200 N/m is compressed by 0.1 m. What is the elastic potential energy stored?

  1. 10 J
  2. 1 J Correct answer.
  3. 2 J
  4. 0.5 J

Explanation

Elastic potential energy in a spring is ½kx². Substituting k = 200 N/m and x = 0.1 m gives ½ × 200 × 0.01 = 1 J of stored energy.

Question 37Physics

The time period of a body executing simple harmonic motion is 0.4 s. What is the angular frequency of the motion?

  1. 5π rad/s Correct answer.
  2. 0.4π rad/s
  3. 0.8 rad/s
  4. 2.5 rad/s

Explanation

Angular frequency is related to time period by ω = 2π/T. With T = 0.4 s, ω = 2π/0.4 = 5π rad/s, which is about 15.7 rad/s.

Question 38Physics

A pipe closed at one end resonates in its fundamental mode with a frequency of 250 Hz. Taking the speed of sound as 340 m/s, what is the length of the pipe?

  1. 1.36 m
  2. 0.34 m Correct answer.
  3. 0.17 m
  4. 0.68 m

Explanation

A closed pipe supports a quarter wavelength in its fundamental mode, so f = v/(4L). Rearranging gives L = v/(4f) = 340/(4 × 250) = 0.34 m.

Question 39Physics

An ideal gas is compressed adiabatically. Which statement describes the change in its internal energy?

  1. Internal energy increases because work is done on the gas Correct answer.
  2. Internal energy increases because heat is supplied to the gas
  3. Internal energy stays constant because no heat is exchanged
  4. Internal energy decreases because heat leaves the gas

Explanation

In an adiabatic process ΔQ = 0, so the first law reduces to ΔU = −ΔW. Compressing the gas means work is done on it (ΔW negative), so ΔU is positive and the temperature rises.

Question 40Physics

A gas at 27 °C is heated at constant pressure until its volume doubles. What is its final temperature?

  1. 300 °C
  2. 54 °C
  3. 600 °C
  4. 327 °C Correct answer.

Explanation

At constant pressure, Charles's law gives V/T constant, so the absolute temperature must double. The initial temperature is 300 K, so the final value is 600 K, which is 600 − 273 = 327 °C.

Question 41Physics

Two capacitors of 3 μF and 6 μF are connected in series across a 12 V supply. What is the charge on each capacitor?

  1. 24 μC Correct answer.
  2. 12 μC
  3. 108 μC
  4. 36 μC

Explanation

For series capacitors, 1/C = 1/3 + 1/6 = 1/2, so C = 2 μF. The charge is Q = CV = 2 × 12 = 24 μC, and capacitors in series carry equal charge.

Question 42Physics

An ideal 12 V battery supplies 12 Ω and 6 Ω resistors connected in parallel. The 6 Ω branch is removed. How does the battery current change?

  1. From 3 A to 1 A Correct answer.
  2. From 2 A to 1 A
  3. From 3 A to 2 A
  4. It stays 3 A

Explanation

Initially the branch currents are 12/12=1 A and 12/6=2 A, totaling 3 A. Removing the 6 Ω branch leaves only the 12 Ω resistor drawing 1 A.

Question 43Physics

A charged particle enters a uniform magnetic field with its velocity parallel to the field. What is the path of the particle?

  1. A straight line Correct answer.
  2. A parabola
  3. A circle
  4. A helix

Explanation

The magnetic force is qvB sin θ, and θ = 0 here, so the force is zero. With no force the particle continues along a straight line at constant speed.

Question 44Physics

A charged particle is accelerated through a potential difference V from rest. If V is doubled, the kinetic energy gained by the particle becomes

  1. twice the original value Correct answer.
  2. unchanged
  3. four times the original value
  4. half the original value

Explanation

The work done on a charge q by a potential difference V is qV, so the kinetic energy gained is directly proportional to V. Doubling V therefore doubles the kinetic energy, though the speed increases only by a factor of √2.

Question 45Physics

In a series LCR circuit at resonance, what is the phase difference between the applied voltage and the current?

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

Explanation

At resonance the inductive reactance X_L equals the capacitive reactance X_C, so they cancel and the impedance is purely resistive. The current is then in phase with the applied voltage, giving a phase difference of zero.

Question 46Physics

An electron and a proton are accelerated through the same potential difference. Which particle has the shorter de Broglie wavelength?

  1. The electron
  2. It depends on the direction of acceleration
  3. Both have the same wavelength
  4. The proton Correct answer.

Explanation

For equal kinetic energy qV, the de Broglie wavelength is λ = h/√(2mK), so it varies inversely as the square root of mass. The proton is about 1836 times heavier than the electron, so its wavelength is shorter.

Question 47Physics

The work function of a metal is 2.0 eV. Light of photon energy 3.5 eV falls on it. What is the maximum kinetic energy of the emitted photoelectrons?

  1. 1.5 eV Correct answer.
  2. 7.0 eV
  3. 5.5 eV
  4. 1.75 eV

Explanation

Einstein's photoelectric equation gives K_max = hν − φ. Substituting the given values, K_max = 3.5 − 2.0 = 1.5 eV, which is the energy carried away by the most energetic electrons.

Question 48Physics

A radioactive nucleus emits one alpha particle and then one beta particle. How do its mass number and atomic number change overall?

  1. Mass number is unchanged, atomic number decreases by 1
  2. Mass number decreases by 4, atomic number decreases by 1 Correct answer.
  3. Mass number decreases by 4, atomic number decreases by 3
  4. Mass number decreases by 2, atomic number decreases by 1

Explanation

An alpha particle removes 4 nucleons and 2 protons, so A falls by 4 and Z falls by 2. A subsequent beta-minus emission converts a neutron into a proton, raising Z by 1 while leaving A unchanged, giving a net fall of 4 in A and 1 in Z.

Question 49Physics

In a semiconductor, the energy gap between the valence band and the conduction band is about 1.1 eV at room temperature. Which statement about its conductivity is correct?

  1. It is independent of temperature because the gap is fixed
  2. It increases with rising temperature because more electron-hole pairs are created Correct answer.
  3. It decreases with rising temperature because lattice vibrations scatter carriers more strongly
  4. It becomes zero above room temperature

Explanation

In a semiconductor the number of charge carriers rises rapidly with temperature as electrons are thermally excited across the gap. This increase in carrier concentration outweighs the extra lattice scattering, so conductivity increases.

Question 50Physics

A ray of light passes from glass of refractive index 1.5 into air. What is the critical angle for total internal reflection?

  1. sin⁻¹(1/3)
  2. sin⁻¹(1.5)
  3. cos⁻¹(2/3)
  4. sin⁻¹(2/3) Correct answer.

Explanation

The critical angle satisfies sin C = n₂/n₁ for light going from the denser to the rarer medium. With n₁ = 1.5 and n₂ = 1, sin C = 1/1.5 = 2/3, so C = sin⁻¹(2/3), about 41.8°.