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NEB Class 12 Physics study materials
NEB Class 12 Physics study resources

NEB Class 12 Physics practice questions

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Question 1Mechanics

A body moves in a straight line with uniform acceleration. Which quantity-time graph is a straight line whose slope equals the acceleration?

  1. Acceleration-time graph
  2. Position-time squared graph
  3. Displacement-time graph
  4. Velocity-time graph Correct answer.

Explanation

For uniform acceleration the velocity changes at a constant rate, so plotting velocity against time gives a straight line and its gradient is exactly the acceleration. The displacement-time graph is a curve whose gradient gives velocity, not acceleration.

Question 2Mechanics

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 s?

  1. 30 m
  2. 45 m Correct answer.
  3. 90 m
  4. 15 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 displacement grows with the square of time, not linearly.

Question 3Mechanics

A projectile is launched at an angle to the horizontal with no air resistance. Which statement about its motion is correct?

  1. Horizontal velocity stays constant while vertical velocity changes uniformly Correct answer.
  2. Both horizontal and vertical velocity stay constant
  3. Horizontal velocity changes uniformly while vertical velocity stays constant
  4. Both horizontal and vertical velocity change uniformly with time

Explanation

With no air resistance there is no horizontal force, so the horizontal component of velocity remains constant. The only force is weight acting vertically, giving a constant downward acceleration that changes the vertical velocity uniformly.

Question 4Mechanics

Two forces of 3 N and 4 N act at right angles at a point. What is the magnitude of their resultant?

  1. 7 N
  2. 1 N
  3. 12 N
  4. 5 N Correct answer.

Explanation

Perpendicular vectors add by the parallelogram rule, so the resultant magnitude is √(3² + 4²) = √25 = 5 N. Simple addition would only apply if the forces were parallel.

Question 5Mechanics

A body moves in a circle at constant speed. Which quantity remains constant during the motion?

  1. Velocity
  2. Speed Correct answer.
  3. Momentum vector
  4. Acceleration vector

Explanation

In uniform circular motion the magnitude of velocity, which is the speed, stays constant. Velocity, acceleration and momentum are vectors whose directions change continuously as the body goes round.

Question 6Mechanics

State Newton's first law of motion in terms of force.

  1. Every action has an equal and opposite reaction
  2. Force equals the rate of change of momentum
  3. A body stays at rest or in uniform motion unless a net external force acts on it Correct answer.
  4. A body always moves in the direction of the net force

Explanation

The first law defines inertia: with zero net external force, a body keeps its state of rest or uniform straight-line motion. It also implies that a net force is needed to change that state.

Question 7Mechanics

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

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

Explanation

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

Question 8Mechanics

Which quantity is a scalar?

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

Explanation

Work is defined as the dot product of force and displacement, so it has magnitude but no direction and is a scalar. Force, displacement and acceleration are all vectors.

Question 9Mechanics

A car accelerates uniformly from 10 m/s to 30 m/s in 5 s. What is its acceleration?

  1. 4 m/s² Correct answer.
  2. 6 m/s²
  3. 8 m/s²
  4. 2 m/s²

Explanation

Acceleration is the change in velocity divided by the time taken: (30 − 10)/5 = 4 m/s². Using the final velocity alone or the average velocity gives incorrect values.

Question 10Mechanics

A ball is thrown vertically upward with speed u. Ignoring air resistance, what is its speed when it returns to the point of projection?

  1. u/2
  2. Zero
  3. u Correct answer.
  4. 2u

Explanation

Gravity is conservative, so the ball regains the same kinetic energy on returning to the same height, giving the same speed u. Only the direction of motion is reversed, not the magnitude.

Question 11Mechanics

A projectile is fired with speed u at 45° to the horizontal. Taking g = 10 m/s², what is its maximum height when u = 20 m/s?

  1. 5 m
  2. 10 m Correct answer.
  3. 40 m
  4. 20 m

Explanation

The vertical component is u sin45° = 20 × 0.707 ≈ 14.1 m/s, and maximum height is (u sinθ)²/(2g) = 200/20 = 10 m. Only the vertical component determines the height.

Question 12Mechanics

A force F = (6i + 8j) N acts on a body that undergoes displacement d = (3i + 0j) m. What is the work done by the force?

  1. 10 J
  2. 24 J
  3. 30 J
  4. 18 J Correct answer.

Explanation

Work is the dot product F·d = (6)(3) + (8)(0) = 18 J. Only the component of force along the displacement does work.

Question 13Mechanics

A body of mass 2 kg moves at 3 m/s. What is its kinetic energy?

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

Explanation

Kinetic energy is ½mv² = ½ × 2 × 9 = 9 J. The square of the speed, not the speed itself, enters the formula.

Question 14Mechanics

A block of mass m slides down a smooth incline of height h from rest. What is its speed at the bottom?

  1. √(gh)
  2. 2gh
  3. √(2gh) Correct answer.
  4. gh

Explanation

Loss of potential energy mgh equals gain in kinetic energy ½mv², so v² = 2gh and v = √(2gh). The result is independent of the incline angle.

Question 15Mechanics

Two bodies of masses m and 2m have equal kinetic energies. What is the ratio of their momenta, p(small m) : p(large mass)?

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

Explanation

Since p = √(2mK), for equal K the momentum is proportional to √m, so the ratio is √m : √(2m) = 1 : √2. The lighter body has less momentum for the same kinetic energy.

Question 16Mechanics

A body moves in a circle of radius r at constant speed v. What is its centripetal acceleration?

  1. vr
  2. r/v²
  3. v/r²
  4. v²/r Correct answer.

Explanation

The centripetal acceleration has magnitude v²/r and points towards the centre of the circle. It arises because the direction of velocity changes continuously.

Question 17Mechanics

A satellite orbits a planet in a circular path. If the orbital radius is doubled while the speed is unchanged, what happens to the required centripetal force?

  1. It becomes four times larger
  2. It halves Correct answer.
  3. It stays the same
  4. It doubles

Explanation

The centripetal force is mv²/r, so for fixed mass and speed it is inversely proportional to radius. Doubling r therefore halves the required force.

Question 18Mechanics

A block of mass 5 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. 20 N Correct answer.
  2. 25 N
  3. 2 N
  4. 50 N

Explanation

The limiting friction is μN = μmg = 0.4 × 5 × 10 = 20 N. Static friction can take any value up to this limit depending on the applied force.

Question 19Mechanics

Two blocks of masses 3 kg and 2 kg are connected by a light string over a frictionless pulley. Taking g = 10 m/s², what is the acceleration of the system?

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

Explanation

The net driving force is the weight difference (3 − 2) × 10 = 10 N and the total mass moved is 5 kg, so a = 10/5 = 2 m/s². The heavier block descends and the lighter rises.

Question 20Mechanics

A body of mass 0.5 kg moving at 4 m/s collides with a stationary body of mass 0.5 kg and they stick together. What is the common velocity after collision?

  1. 1 m/s
  2. 4 m/s
  3. 0.5 m/s
  4. 2 m/s Correct answer.

Explanation

Momentum is conserved in the perfectly inelastic collision: 0.5 × 4 = (0.5 + 0.5)v, giving v = 2 m/s. Kinetic energy is not conserved, but momentum is.

Question 21Mechanics

A body of mass 2 kg is at rest. A constant force of 6 N acts on it for 4 s. What is the change in its momentum?

  1. 12 kg m/s
  2. 24 kg m/s Correct answer.
  3. 48 kg m/s
  4. 3 kg m/s

Explanation

Impulse equals change in momentum: F × t = 6 × 4 = 24 kg m/s. The mass is not needed because impulse directly gives the momentum change.

Question 22Mechanics

A flywheel of moment of inertia 2 kg m² rotates at 5 rad/s. What is its rotational kinetic energy?

  1. 50 J
  2. 5 J
  3. 10 J
  4. 25 J Correct answer.

Explanation

Rotational kinetic energy is ½Iω² = ½ × 2 × 25 = 25 J. The angular speed is squared, just as linear speed is in translational kinetic energy.

Question 23Mechanics

A solid sphere and a hollow cylinder of the same mass and radius roll down the same incline from rest without slipping. Which reaches the bottom first?

  1. Both reach together
  2. It depends on the length of the incline
  3. The hollow cylinder
  4. The solid sphere Correct answer.

Explanation

Rolling acceleration depends on the moment of inertia factor: a = g sinθ/(1 + I/mr²). The solid sphere has the smaller factor (2/5) compared with the hollow cylinder (1), so it accelerates faster and arrives first.

Question 24Mechanics

A body of mass m is attached to a string and whirled in a vertical circle of radius r. At the highest point, what is the minimum speed for the string to stay taut?

  1. √(gr/2)
  2. √(gr) Correct answer.
  3. gr
  4. √(2gr)

Explanation

At the top the weight provides the centripetal force when tension just vanishes, so mg = mv²/r, giving v = √(gr). Any smaller speed would make the string go slack.

Question 25Mechanics

A particle moves under a conservative force field. Which statement about its mechanical energy is correct?

  1. Total mechanical energy always decreases
  2. Potential energy alone is constant
  3. Total mechanical energy is constant throughout the motion Correct answer.
  4. Kinetic energy alone is constant

Explanation

For a conservative field the work done by the force depends only on the endpoints, so kinetic and potential energy interchange but their sum stays constant. Friction, which is non-conservative, would be needed for a decrease.

Question 26Mechanics

A body moves in a straight line such that its velocity-time graph is a horizontal straight line above the time axis. Which statement describes the motion of the body?

  1. It moves with uniform velocity and zero acceleration. Correct answer.
  2. It moves with uniform acceleration and increasing velocity.
  3. It moves with decreasing acceleration and constant displacement.
  4. It moves with zero velocity and constant acceleration.

Explanation

The slope of a velocity-time graph gives acceleration, and a horizontal line has zero slope, so acceleration is zero. The constant height of the line shows the velocity is constant and non-zero. Hence the body moves with uniform velocity along a straight line.

Question 27Mechanics

A body is dropped from rest from a height and falls freely under gravity. Taking g = 10 m/s² and ignoring air resistance, how far does it fall in the third second of its motion?

  1. 45 m
  2. 20 m
  3. 5 m
  4. 25 m Correct answer.

Explanation

The distance fallen in the nth second from rest is s = u + (g/2)(2n − 1), with u = 0 and n = 3. This gives s = 5 × 5 = 25 m. Equivalently, total fall in 3 s is 45 m and in 2 s is 20 m, and the difference is 25 m.

Question 28Mechanics

A particle moves in a circle of radius 2 m with a constant angular speed of 3 rad/s. What is the magnitude of its centripetal acceleration?

  1. 12 m/s²
  2. 18 m/s² Correct answer.
  3. 36 m/s²
  4. 6 m/s²

Explanation

Centripetal acceleration is a = ω²r for uniform circular motion, where ω is the angular speed and r the radius. Substituting ω = 3 rad/s and r = 2 m gives a = 9 × 2 = 18 m/s². The tangential speed v = ωr = 6 m/s would give the same result through v²/r.

Question 29Mechanics

A rigid body rotates about a fixed axis with constant angular acceleration. Which statement about the body at a given instant is correct?

  1. All points of the body have the same angular velocity but different linear speeds. Correct answer.
  2. All points of the body have the same linear speed.
  3. Points farther from the axis have smaller linear speeds than points nearer the axis.
  4. The angular velocity of a point depends on its distance from the axis.

Explanation

In rigid-body rotation every point turns through the same angle in the same time, so all points share the same angular velocity and angular acceleration. The linear speed, however, is v = ωr, so it grows with distance from the axis. Thus angular quantities are common to the body while linear speeds differ.

Question 30Mechanics

A body of mass 4 kg initially at rest is acted on by a constant force of 12 N for 5 s. What is the work done by the force during this interval?

  1. 60 J
  2. 450 J Correct answer.
  3. 900 J
  4. 180 J

Explanation

The acceleration is a = F/m = 12/4 = 3 m/s², and from rest the displacement in 5 s is s = ½at² = ½ × 3 × 25 = 37.5 m. Work is W = Fs = 12 × 37.5 = 450 J. The work-energy check gives ½mv² = ½ × 4 × 15² = 450 J.

Question 31Mechanics

A uniform metre rule is pivoted at its centre and is in equilibrium. A 20 g mass is hung 30 cm to the left of the pivot. Where must a 30 g mass be hung to keep the rule horizontal?

  1. 30 cm to the right of the pivot
  2. 45 cm to the right of the pivot
  3. 15 cm to the right of the pivot
  4. 20 cm to the right of the pivot Correct answer.

Explanation

For rotational equilibrium about the pivot the clockwise and anticlockwise moments must balance, so m₁d₁ = m₂d₂. Taking 20 × 30 = 30 × d₂ gives d₂ = 20 cm on the opposite side. The masses are placed on opposite sides of the pivot, so the 30 g mass hangs 20 cm to the right.

Question 32Mechanics

A body of mass m moving with speed v collides head-on and elastically with an identical body at rest. Which statement about the velocities after the collision is correct?

  1. The incident body stops and the target body moves off with speed v. Correct answer.
  2. Both bodies move together with speed v/2.
  3. The incident body rebounds with speed v and the target body remains at rest.
  4. Both bodies move with speed v in the original direction.

Explanation

In a one-dimensional elastic collision between equal masses, momentum and kinetic energy conservation together give an exchange of velocities. The incident body therefore comes to rest and the target body moves off with speed v. This is the standard result for equal masses with the second initially at rest.

Question 33Mechanics

A planet moves in an elliptical orbit around the Sun, with the Sun at one focus. Which statement about the planet's motion is correct?

  1. Its angular momentum about the Sun changes as it moves along the orbit.
  2. Its speed is greatest when it is nearest the Sun, and its angular momentum about the Sun stays constant. Correct answer.
  3. Its kinetic energy is the same at every point of the orbit.
  4. Its speed is greatest when it is farthest from the Sun.

Explanation

The gravitational force on the planet acts along the line joining it to the Sun, so its torque about the Sun is zero and angular momentum is conserved. Conservation of angular momentum, mr²ω = constant, means the speed is greatest at perihelion where r is smallest. Kepler's second law expresses this equal-area result.

Question 34Mechanics

A body of mass 2 kg is lifted vertically at constant velocity through a height of 5 m. Taking g = 10 m/s², what is the work done against gravity?

  1. 100 J Correct answer.
  2. 25 J
  3. 10 J
  4. 50 J

Explanation

Work done against gravity equals the gain in gravitational potential energy, mgh. Substituting m = 2 kg, g = 10 m/s² and h = 5 m gives 2 × 10 × 5 = 100 J. Because the body moves at constant velocity, the lifting force equals its weight and no kinetic energy is gained.

Question 35Heat and Thermodynamics

In an isothermal expansion of an ideal gas, which quantity remains unchanged by definition of an isothermal process?

  1. Pressure of the gas
  2. Volume of the gas
  3. Internal energy of the gas
  4. Temperature of the gas Correct answer.

Explanation

Isothermal means the temperature is held constant throughout the process. For an ideal gas, internal energy also stays constant because it depends only on temperature, but constant temperature is the defining condition of an isothermal process.

Question 36Heat and Thermodynamics

The first law of thermodynamics for a system is written as dQ = dU + dW. In this convention, what does dW represent?

  1. Change in internal energy
  2. Heat absorbed by the system
  3. Work done by the system on its surroundings Correct answer.
  4. Work done on the system by the surroundings

Explanation

In the standard sign convention, dQ is heat supplied to the system and dU is the rise in internal energy. The remaining term dW is then the work done by the system, for example expansion work against external pressure.

Question 37Heat and Thermodynamics

A gas is taken from state A to state B by two different paths. Which quantity has the same value along both paths?

  1. Heat absorbed by the gas
  2. Change in internal energy Correct answer.
  3. Work done by the gas
  4. Sum of work done and heat absorbed

Explanation

Internal energy is a state function, so its change depends only on the initial and final states and not on the route taken. Work and heat are path functions and generally differ between the two routes.

Question 38Heat and Thermodynamics

What is the efficiency of a Carnot engine working between a source at 500 K and a sink at 300 K?

  1. 0.20
  2. 0.60
  3. 0.75
  4. 0.40 Correct answer.

Explanation

Carnot efficiency is 1 - T2/T1 with absolute temperatures. Here 1 - 300/500 = 1 - 0.6 = 0.40, that is 40 percent.

Question 39Heat and Thermodynamics

Which statement about the coefficient of volume expansion of a solid is correct?

  1. It is twice the coefficient of linear expansion.
  2. It equals the coefficient of linear expansion.
  3. It is half the coefficient of linear expansion.
  4. It is three times the coefficient of linear expansion. Correct answer.

Explanation

For an isotropic solid the volume expansion coefficient gamma is related to the linear coefficient alpha by gamma = 3 alpha. This follows because volume scales as the cube of a linear dimension.

Question 40Heat and Thermodynamics

A body cools from 80 degrees Celsius to 70 degrees Celsius in 5 minutes in surroundings at 20 degrees Celsius. Using Newton's law of cooling, the approximate time to cool from 70 degrees Celsius to 60 degrees Celsius is

  1. 6 minutes Correct answer.
  2. 4 minutes
  3. 10 minutes
  4. 5 minutes

Explanation

Newton's law gives a cooling rate proportional to the excess of mean temperature over surroundings. The mean excess falls from about 55 K to about 45 K, so the rate drops and the next 10 K takes longer, roughly 5 times 55/45, about 6 minutes.

Question 41Heat and Thermodynamics

For an ideal gas, the molar specific heat at constant pressure Cp is greater than that at constant volume Cv because

  1. the temperature rise is smaller at constant pressure
  2. the gas does external work when heated at constant pressure Correct answer.
  3. the internal energy rises only at constant pressure
  4. the number of molecules increases on heating

Explanation

At constant pressure, part of the supplied heat goes into expansion work against the surroundings, so more heat is needed for the same temperature rise. Hence Cp exceeds Cv by the gas constant R for one mole.

Question 42Heat and Thermodynamics

The average kinetic energy of a molecule of an ideal gas at absolute temperature T is

  1. (1/2)kT
  2. (3/2)RT
  3. kT
  4. (3/2)kT Correct answer.

Explanation

Kinetic theory gives the mean translational kinetic energy per molecule as (3/2)kT, where k is the Boltzmann constant. Each of the three translational degrees of freedom contributes (1/2)kT.

Question 43Heat and Thermodynamics

An ideal gas undergoes an adiabatic expansion. Which statement about the process is correct?

  1. Heat flows into the gas to keep the temperature constant.
  2. The pressure stays constant while the volume increases.
  3. The internal energy of the gas stays constant.
  4. No heat enters or leaves the gas, and the gas cools. Correct answer.

Explanation

Adiabatic means Q = 0, so the gas does expansion work at the expense of its internal energy. Since internal energy falls, the temperature of the gas decreases.

Question 44Heat and Thermodynamics

A gas expands at constant pressure of 2.0 x 10^5 Pa from 1.0 x 10^-3 m^3 to 3.0 x 10^-3 m^3. The work done by the gas is

  1. 400 J Correct answer.
  2. 600 J
  3. 200 J
  4. 800 J

Explanation

Work at constant pressure is p times the change in volume. The volume change is 2.0 x 10^-3 m^3, so W = 2.0 x 10^5 times 2.0 x 10^-3 = 400 J.

Question 45Heat and Thermodynamics

A Carnot refrigerator extracts heat from a cold reservoir at 250 K and rejects heat to surroundings at 300 K. Its coefficient of performance is

  1. 6.0
  2. 5.0 Correct answer.
  3. 1.2
  4. 0.20

Explanation

For a Carnot refrigerator the coefficient of performance is T2/(T1 - T2), where T2 is the cold temperature. Thus 250/(300 - 250) = 250/50 = 5.0.

Question 46Heat and Thermodynamics

Two rods of the same length and cross-section, with thermal conductivities in the ratio 1:2, are joined end to end. If the free ends are at 100 degrees Celsius and 0 degrees Celsius, the temperature at the junction in steady state is

  1. 25 degrees Celsius
  2. 67 degrees Celsius
  3. 50 degrees Celsius
  4. 33 degrees Celsius Correct answer.

Explanation

In series the same heat current flows through both rods, so the temperature drop is inversely proportional to conductivity. With conductivities 1:2 the drops are in ratio 2:1, giving a drop of about 67 K across the first rod and a junction near 33 degrees Celsius.

Question 47Heat and Thermodynamics

A black body radiates energy at a rate proportional to the fourth power of its absolute temperature. If its absolute temperature is doubled, the radiated power becomes

  1. 4 times
  2. 2 times
  3. 16 times Correct answer.
  4. 8 times

Explanation

By the Stefan-Boltzmann law the power per unit area is proportional to T^4. Doubling T multiplies T^4 by 2^4 = 16, so the radiated power increases sixteen-fold.

Question 48Heat and Thermodynamics

The root mean square speed of molecules of a gas is v at temperature T. If the absolute temperature is raised to 4T at constant volume, the rms speed becomes

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

Explanation

The rms speed is proportional to the square root of absolute temperature, since (1/2)m v_rms^2 = (3/2)kT. Raising T to 4T multiplies the square root by 2, so the speed becomes 2v.

Question 49Heat and Thermodynamics

In a cyclic process, a system absorbs 600 J of heat and does 200 J of work. What is the net change in its internal energy over one complete cycle?

  1. 0 J Correct answer.
  2. 800 J
  3. 400 J
  4. 200 J

Explanation

For a complete cycle the system returns to its initial state, so the change in internal energy is zero. The first law then requires that the net heat absorbed equals the net work done, which is consistent with the 400 J difference being rejected as heat.

Question 50Heat and Thermodynamics

A real gas is being liquefied. Which behaviour is required for the gas to be liquefiable by compression alone?

  1. Its pressure must be below the critical pressure at any temperature.
  2. Its temperature must be below its critical temperature. Correct answer.
  3. It must behave exactly as an ideal gas.
  4. Its temperature must be above its critical temperature.

Explanation

Above the critical temperature a gas cannot be liquefied by pressure alone, however great. Liquefaction by compression therefore requires the gas to be cooled below its critical temperature first.