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WBBSE Madhyamik Physical Science study materials
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WBBSE Madhyamik Physical Science practice questions

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Question 1Measurement and Motion (Physics)

Which of the following is the SI base unit of length?

  1. kilometre
  2. metre Correct answer.
  3. centimetre
  4. millimetre

Explanation

The metre is the SI base unit of length and is defined in terms of the speed of light in vacuum. The centimetre, millimetre and kilometre are decimal multiples or submultiples of the metre, so they are derived practical units rather than base units.

Question 2Measurement and Motion (Physics)

The dimensional formula of speed is

  1. [M L T⁻¹]
  2. [L T⁻²]
  3. [M L T⁻²]
  4. [L T⁻¹] Correct answer.

Explanation

Speed is the distance travelled per unit time, so its dimension is length divided by time, written [L T⁻¹]. Mass does not appear anywhere in the definition of speed, which rules out any formula containing [M].

Question 3Measurement and Motion (Physics)

A body is said to be in uniform motion along a straight line when it

  1. covers unequal distances in equal intervals of time
  2. covers equal distances in equal intervals of time Correct answer.
  3. comes to rest after equal intervals of time
  4. changes its direction at regular intervals of time

Explanation

Uniform motion along a straight line means the body covers equal distances in equal intervals of time, however small those intervals are taken. In such motion the speed stays constant and the direction does not change, so the body has zero acceleration.

Question 4Measurement and Motion (Physics)

A vernier calliper has a main scale division of 1 mm, and 10 vernier scale divisions coincide with 9 main scale divisions. Its least count is

  1. 1 mm
  2. 0.5 mm
  3. 0.1 mm Correct answer.
  4. 0.05 mm

Explanation

The least count is one main scale division minus one vernier scale division. Since 10 vernier divisions equal 9 main scale divisions, one vernier division is 0.9 mm, so the least count is 1 mm − 0.9 mm = 0.1 mm.

Question 5Measurement and Motion (Physics)

The pitch of a screw gauge is 0.5 mm and its circular scale has 50 divisions. The least count of the instrument is

  1. 0.5 mm
  2. 0.05 mm
  3. 0.1 mm
  4. 0.01 mm Correct answer.

Explanation

The least count of a screw gauge equals the pitch divided by the number of circular scale divisions. Substituting pitch = 0.5 mm and 50 circular divisions gives 0.5 ÷ 50 = 0.01 mm, which is the smallest length the gauge can measure.

Question 6Measurement and Motion (Physics)

A car starts from rest and moves with a uniform acceleration of 2 m/s². The distance covered by it in 5 s is

  1. 50 m
  2. 10 m
  3. 25 m Correct answer.
  4. 20 m

Explanation

Use the equation s = ut + ½at² with u = 0, a = 2 m/s² and t = 5 s. Then s = 0 + ½ × 2 × 25 = 25 m, so the car travels 25 m in the first five seconds.

Question 7Measurement and Motion (Physics)

A cyclist moves along a circular track of radius 7 m and completes half a revolution. Taking π = 22/7, the ratio of the distance covered to the magnitude of the displacement is

  1. 1 : 1
  2. 7 : 11
  3. 11 : 7 Correct answer.
  4. 22 : 7

Explanation

The distance along the semicircular path is πr = (22/7) × 7 = 22 m, while the displacement is the diameter, 2r = 14 m. Their ratio is 22 : 14, which simplifies to 11 : 7.

Question 8Measurement and Motion (Physics)

For a body moving along a straight line, the area enclosed between its velocity–time graph and the time axis gives

  1. displacement Correct answer.
  2. acceleration
  3. change in velocity
  4. average velocity

Explanation

The area under a velocity–time graph carries the unit (m/s) × s = m, and therefore represents the displacement of the body in that interval. The slope of the same graph, on the other hand, gives the acceleration.

Question 9Measurement and Motion (Physics)

A bus covers the first half of a journey at 30 km/h and the second half at 60 km/h. Its average speed for the whole journey is

  1. 36 km/h
  2. 45 km/h
  3. 48 km/h
  4. 40 km/h Correct answer.

Explanation

When equal distances are covered at two speeds, the average speed is 2v₁v₂/(v₁ + v₂). Here that gives 2 × 30 × 60 ÷ 90 = 40 km/h, because the slower half of the journey takes twice as long as the faster half.

Question 10Measurement and Motion (Physics)

A ball is thrown vertically upwards with a speed of 20 m/s. Taking g = 10 m/s² and neglecting air resistance, the maximum height reached by the ball is

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

Explanation

At the highest point the velocity becomes zero, so v² = u² − 2gh with v = 0 gives h = u²/2g. Substituting u = 20 m/s and g = 10 m/s² gives h = 400 ÷ 20 = 20 m.

Question 11Measurement and Motion (Physics)

Which of the following quantities is a scalar in the study of motion?

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

Explanation

Speed has magnitude only and no direction, so it is a scalar quantity. Displacement, velocity and acceleration are vectors because each requires a direction as well as a magnitude.

Question 12Measurement and Motion (Physics)

Which of these is an SI base quantity?

  1. Speed
  2. Mass Correct answer.
  3. Pressure
  4. Force

Explanation

In the SI system, mass is one of the seven base quantities, and its base unit is the kilogram. Force, speed and pressure are derived quantities formed by combining base quantities.

Question 13Measurement and Motion (Physics)

The instrument best suited for measuring the thickness of a thin metal sheet is a

  1. screw gauge Correct answer.
  2. vernier calliper
  3. metre scale
  4. measuring tape

Explanation

A screw gauge uses a finely threaded screw and a circular scale to measure very small thicknesses accurately. A metre scale or measuring tape has a much larger least count and cannot measure a thin sheet precisely.

Question 14Measurement and Motion (Physics)

A student walks 4 m towards east and then 3 m towards north. The total distance travelled and the magnitude of displacement are respectively

  1. 5 m and 7 m
  2. 7 m and 7 m
  3. 7 m and 5 m Correct answer.
  4. 5 m and 5 m

Explanation

Distance is the actual path length, so it is 4 m + 3 m = 7 m. Displacement is the straight-line change in position, and the two displacements are perpendicular, so its magnitude is √(4² + 3²) = 5 m.

Question 15Measurement and Motion (Physics)

The zero of the vernier scale of a calliper lies 3 divisions to the right of the zero of the main scale. If the least count is 0.01 cm, the zero error is

  1. −0.003 cm
  2. +0.003 cm
  3. −0.03 cm
  4. +0.03 cm Correct answer.

Explanation

When the vernier zero lies to the right of the main-scale zero, the zero error is positive. Zero error = number of divisions × least count = 3 × 0.01 cm = +0.03 cm.

Question 16Measurement and Motion (Physics)

A train moving at 72 km/h is brought to rest in 10 s. Its retardation, assumed uniform, is

  1. 0.72 m/s²
  2. 7.2 m/s²
  3. 2 m/s² Correct answer.
  4. 20 m/s²

Explanation

Convert the speed: 72 km/h = 72 × 5/18 = 20 m/s. Using v = u + at gives 0 = 20 + a × 10, so a = −2 m/s²; the retardation is 2 m/s².

Question 17Measurement and Motion (Physics)

For a body moving along a straight line, a velocity–time graph that is a straight line parallel to the time axis at a positive velocity indicates

  1. non-uniform velocity
  2. uniform acceleration
  3. uniform velocity Correct answer.
  4. the body is at rest

Explanation

A horizontal velocity–time line means the velocity does not change with time. Since the line is above the time axis at a positive value, the body moves with constant, or uniform, velocity.

Question 18Measurement and Motion (Physics)

The length and breadth of a rectangle are measured as 5.2 cm and 3.1 cm. The area of the rectangle, expressed to the correct number of significant figures, is

  1. 16.1 cm²
  2. 20 cm²
  3. 16.12 cm²
  4. 16 cm² Correct answer.

Explanation

The product is 5.2 × 3.1 = 16.12 cm². Both measurements have two significant figures, so the area must be rounded to two significant figures, giving 16 cm².

Question 19Measurement and Motion (Physics)

A particle moves once completely around a circular path of radius r in time T. For this complete revolution, its average velocity and average speed are respectively

  1. 2πr/T and 0
  2. 0 and 0
  3. 2πr/T and 2πr/T
  4. 0 and 2πr/T Correct answer.

Explanation

After one complete revolution, the particle returns to its starting point, so its displacement is zero and average velocity is zero. The distance travelled is the circumference 2πr, so average speed is 2πr/T.

Question 20Measurement and Motion (Physics)

The displacement x of a particle moving along a straight line is given by x = 2t² + 3t, where x is in metres and t in seconds. Its velocity at t = 2 s is

  1. 7 m/s
  2. 8 m/s
  3. 14 m/s
  4. 11 m/s Correct answer.

Explanation

Velocity is the rate of change of displacement, so v = dx/dt = 4t + 3. At t = 2 s, v = 4(2) + 3 = 11 m/s.

Question 21Force, Work and Energy (Physics)

The SI unit of work is

  1. pascal
  2. newton
  3. joule Correct answer.
  4. watt

Explanation

Work is the product of force and the displacement measured along the force, so its unit is the newton-metre, which is given the name joule (1 J = 1 N·m). The newton, watt and pascal belong to force, power and pressure respectively.

Question 22Force, Work and Energy (Physics)

A boy pushes a heavy wall with a force of 50 N, but the wall does not move at all. The work done by the boy on the wall is

  1. 500 J
  2. 50 J
  3. 250 J
  4. zero Correct answer.

Explanation

Work done is W = Fs cosθ, where s is the displacement. Since the wall does not move, s = 0, so the work is zero however large the applied force may be.

Question 23Force, Work and Energy (Physics)

One joule of work is said to be done when

  1. a force of 1 N acts on a body for 1 s
  2. a force of 1 N moves a body 1 m along the direction of the force Correct answer.
  3. a mass of 1 kg is lifted vertically through 1 cm
  4. a force of 1 N moves a body 1 cm along the direction of the force

Explanation

By definition, 1 J is the work done when a force of 1 N displaces a body through 1 m in the direction of the force, since 1 N × 1 m = 1 N·m = 1 J.

Question 24Force, Work and Energy (Physics)

A force of 20 N acting at 60° to the horizontal displaces a body 5 m along the horizontal. The work done by the force is

  1. 86.6 J
  2. 25 J
  3. 50 J Correct answer.
  4. 100 J

Explanation

Only the component of the force along the displacement does work, so W = Fs cosθ = 20 × 5 × cos60° = 20 × 5 × 0.5 = 50 J.

Question 25Force, Work and Energy (Physics)

A body of mass 2 kg moves with a speed of 3 m/s. Its kinetic energy is

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

Explanation

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

Question 26Force, Work and Energy (Physics)

A pump lifts 100 kg of water through a height of 10 m in 20 s. Taking g = 10 m/s², the power of the pump is

  1. 500 W Correct answer.
  2. 50 W
  3. 1000 W
  4. 5000 W

Explanation

The work done against gravity is mgh = 100 × 10 × 10 = 10 000 J. Power is work divided by time, so P = 10 000/20 = 500 W.

Question 27Force, Work and Energy (Physics)

A body of mass 5 kg is raised to a height of 4 m. Taking g = 10 m/s², the gain in its gravitational potential energy is

  1. 20 J
  2. 50 J
  3. 200 J Correct answer.
  4. 100 J

Explanation

The gain in gravitational potential energy is mgh = 5 × 10 × 4 = 200 J, measured with respect to the starting level.

Question 28Force, Work and Energy (Physics)

A ball is dropped from rest from a height h above the ground. Ignoring air resistance, its kinetic energy when it has fallen through half the height is

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

Explanation

During the fall the total mechanical energy stays constant. In falling through h/2 the ball loses potential energy mg(h/2), and this appears entirely as kinetic energy, so the kinetic energy is mgh/2.

Question 29Force, Work and Energy (Physics)

A pump raises 10 kg of water per second through a height of 5 m and delivers it with a speed of 2 m/s. Taking g = 10 m/s², the power of the pump is

  1. 540 W
  2. 500 W
  3. 20 W
  4. 520 W Correct answer.

Explanation

Each second the pump gives the water potential energy 10 × 10 × 5 = 500 J and kinetic energy ½ × 10 × 2² = 20 J. The total energy supplied per second is 520 J, so the power is 520 W.

Question 30Force, Work and Energy (Physics)

A body moving with speed v is brought to rest by a constant retarding force after travelling a distance s. If the same body moves with speed 2v and the same retarding force acts, the stopping distance becomes

  1. 8s
  2. 2s
  3. s/2
  4. 4s Correct answer.

Explanation

By the work–energy theorem, the retarding force times the stopping distance equals the initial kinetic energy: Fs = ½mv². With the same force, s is proportional to v², so doubling the speed makes the stopping distance four times as large.

Question 31Force, Work and Energy (Physics)

Which of the following is the SI unit of power?

  1. watt Correct answer.
  2. pascal
  3. newton
  4. joule

Explanation

Power is the rate of doing work, so its unit is the joule per second, which is called the watt. Therefore 1 W = 1 J/s.

Question 32Force, Work and Energy (Physics)

A coolie carrying a load on his head walks along a horizontal road at constant speed. The work done by the upward force exerted by the coolie on the load is

  1. positive, because the load moves forward
  2. negative, because gravity acts downward
  3. zero, because the force is perpendicular to the displacement Correct answer.
  4. equal to the weight of the load multiplied by the distance walked

Explanation

Work done by a force is Fs cos θ, where θ is the angle between the force and the displacement. The upward force on the load is vertical while the displacement is horizontal, so θ = 90° and cos 90° = 0. Hence this force does no work on the load.

Question 33Force, Work and Energy (Physics)

The commercial unit of electrical energy, 1 kWh, is equal to

  1. 3.6 × 10⁶ J Correct answer.
  2. 3.6 × 10⁴ J
  3. 3.6 × 10⁷ J
  4. 3.6 × 10³ J

Explanation

1 kW = 1000 W and 1 hour = 3600 s. Therefore 1 kWh = 1000 × 3600 J = 3.6 × 10⁶ J.

Question 34Force, Work and Energy (Physics)

A body of mass 2 kg has a momentum of 8 kg·m/s. Its kinetic energy is

  1. 8 J
  2. 4 J
  3. 16 J Correct answer.
  4. 32 J

Explanation

From p = mv, the speed is v = p/m = 8/2 = 4 m/s. Then kinetic energy is ½mv² = ½ × 2 × 4² = 16 J. Equivalently, K = p²/(2m) = 64/4 = 16 J.

Question 35Force, Work and Energy (Physics)

A stone of mass 0.5 kg falls freely from rest through a vertical distance of 20 m. Taking g = 10 m/s² and ignoring air resistance, the work done by gravity on the stone is

  1. 50 J
  2. 10 J
  3. 200 J
  4. 100 J Correct answer.

Explanation

The gravitational force is mg = 0.5 × 10 = 5 N, and it acts in the same direction as the 20 m displacement. Hence work done by gravity = mgh = 0.5 × 10 × 20 = 100 J, and it is positive.

Question 36Force, Work and Energy (Physics)

A pump of power 2 kW lifts water through a vertical height of 10 m. Taking g = 10 m/s², the time required to lift 500 kg of water is

  1. 50 s
  2. 5 s
  3. 250 s
  4. 25 s Correct answer.

Explanation

The useful work needed is mgh = 500 × 10 × 10 = 50,000 J. Since power = work/time, time = work/power = 50,000/2000 = 25 s.

Question 37Force, Work and Energy (Physics)

A body is thrown vertically upward with a speed of 20 m/s. Taking g = 10 m/s² and ignoring air resistance, at what height above the point of projection is its kinetic energy equal to half of its initial kinetic energy?

  1. 20 m
  2. 10 m Correct answer.
  3. 5 m
  4. 15 m

Explanation

Kinetic energy is proportional to v², so half the initial kinetic energy means v² = u²/2. Using v² = u² − 2gh gives h = u²/(4g) = 400/40 = 10 m.

Question 38Force, Work and Energy (Physics)

A crane lifts a load of mass 200 kg vertically upward at a constant speed of 0.5 m/s. Taking g = 10 m/s², the power delivered by the crane is

  1. 1000 W Correct answer.
  2. 500 W
  3. 100 W
  4. 2000 W

Explanation

At constant speed, the upward force exerted by the crane equals the weight, F = mg = 200 × 10 = 2000 N. Power = force × velocity = 2000 × 0.5 = 1000 W.

Question 39Force, Work and Energy (Physics)

A body is displaced along a straight line by a force whose magnitude varies with displacement as follows: the force is constant at 20 N from 0 m to 5 m, then decreases uniformly to zero at 10 m. The total work done by the force is

  1. 50 J
  2. 100 J
  3. 200 J
  4. 150 J Correct answer.

Explanation

Work done is the area under the force–displacement graph. The rectangular part gives 20 × 5 = 100 J, and the triangular part gives ½ × 5 × 20 = 50 J. Thus the total work is 100 + 50 = 150 J.

Question 40Force, Work and Energy (Physics)

A simple pendulum bob is released from rest from a horizontal position with the string taut. The length of the pendulum is 1 m. Taking g = 10 m/s² and ignoring air resistance, the speed of the bob at the lowest point is

  1. √20 m/s Correct answer.
  2. √5 m/s
  3. 10 m/s
  4. √10 m/s

Explanation

The bob falls through a vertical height equal to the string length, 1 m, before reaching the lowest point. By conservation of mechanical energy, mgh = ½mv², so v = √(2gh) = √(2 × 10 × 1) = √20 m/s.

Question 41Heat and Thermal Phenomena (Physics)

In SI, the unit of specific heat capacity is

  1. joule per kilogram
  2. kilogram per joule per kelvin
  3. joule per kilogram per kelvin Correct answer.
  4. joule per kelvin

Explanation

Specific heat capacity is the heat required to raise unit mass of a substance through unit temperature, s = Q/(mΔT). With heat in joule, mass in kilogram and temperature change in kelvin, the unit is J kg⁻¹ K⁻¹, often written J/(kg·K). The same number applies to a rise in °C because one Celsius degree equals one kelvin.

Question 42Heat and Thermal Phenomena (Physics)

The heat of the Sun reaches the Earth across space, where there is no material medium. This transfer of heat takes place mainly by

  1. evaporation
  2. convection
  3. radiation Correct answer.
  4. conduction

Explanation

Radiation is transfer of heat as electromagnetic waves, which need no material medium and travel through vacuum at the speed of light. Conduction and convection both require matter to carry energy, so neither can explain energy reaching us across empty space.

Question 43Heat and Thermal Phenomena (Physics)

Water shows an unusual behaviour between 0 °C and 4 °C. At which temperature does water have its greatest density?

  1. −4 °C
  2. 100 °C
  3. 0 °C
  4. 4 °C Correct answer.

Explanation

When water at 0 °C is warmed, it contracts instead of expanding, so its volume decreases and density increases up to 4 °C. Above 4 °C it expands normally and density falls again. Hence water has maximum density, about 1000 kg m⁻³, at 4 °C, which is why ice floats on water.

Question 44Heat and Thermal Phenomena (Physics)

How much heat is needed to raise the temperature of 2 kg of water from 30 °C to 40 °C? (Specific heat capacity of water = 4200 J kg⁻¹ K⁻¹)

  1. 8.4 × 10⁴ J Correct answer.
  2. 4.2 × 10⁴ J
  3. 8.4 × 10⁵ J
  4. 4.2 × 10⁵ J

Explanation

Use Q = mcΔT with m = 2 kg, c = 4200 J kg⁻¹ K⁻¹ and ΔT = 10 K. Then Q = 2 × 4200 × 10 = 84 000 J, that is 8.4 × 10⁴ J. A temperature rise of 10 °C is the same as a rise of 10 K, so the value of ΔT is 10.

Question 45Heat and Thermal Phenomena (Physics)

A straight bimetallic strip is made by riveting a brass strip and an iron strip firmly together and is then heated strongly. The coefficient of linear expansion of brass is greater than that of iron, so the strip

  1. curves with brass on the outer side Correct answer.
  2. remains straight, as both expand alike
  3. curves with iron on the outer side
  4. shortens, since the iron contracts on heating

Explanation

Both metals expand on heating, but brass expands more than iron for the same rise in temperature. The brass therefore becomes the longer member and must lie along the outer, convex side of the bend, while the shorter iron lies on the inner side. This is the principle of the bimetallic thermostat.

Question 46Heat and Thermal Phenomena (Physics)

Equal masses of water and kerosene, both initially at room temperature, are given equal amounts of heat. The kerosene shows a larger rise in temperature because

  1. kerosene has a lower specific heat than water Correct answer.
  2. heat flows faster through kerosene than through water
  3. kerosene has a higher boiling point than water
  4. kerosene has a greater latent heat than water

Explanation

From Q = mcΔT, when Q and m are the same for both liquids, the temperature rise is inversely proportional to the specific heat capacity. Kerosene has a smaller specific heat capacity than water, so the same heat produces a larger ΔT in it. Speed of heat flow and boiling point do not enter this relation.

Question 47Heat and Thermal Phenomena (Physics)

A burn caused by steam at 100 °C is more severe than a burn caused by boiling water at 100 °C because the steam

  1. releases latent heat when it condenses on the skin Correct answer.
  2. travels faster than boiling water
  3. is at a higher temperature than boiling water
  4. has a lower specific heat capacity than water

Explanation

Steam at 100 °C first condenses to water at 100 °C on touching the skin, releasing its large latent heat of vaporisation, about 2260 kJ per kg, in addition to the heat given up as the water cools. Boiling water at the same temperature gives up only the heat released during cooling. Hence steam delivers much more energy to the tissue.

Question 48Heat and Thermal Phenomena (Physics)

Two rods of equal length and cross-section, one of copper and one of iron, are heated at one end and coated with wax at the other. The wax on the copper rod melts first because copper

  1. is a better conductor of heat than iron Correct answer.
  2. has a lower melting point than iron
  3. expands less on heating than iron
  4. has a greater specific heat capacity than iron

Explanation

The rate at which heat travels along a rod depends on the thermal conductivity of the material. Copper has a much higher thermal conductivity than iron, so heat reaches the waxed end sooner and the wax melts earlier. Specific heat capacity and melting point of the metal do not decide this rate.

Question 49Heat and Thermal Phenomena (Physics)

10 g of ice at 0 °C is mixed with 50 g of water at 40 °C in an insulated container. Taking the specific latent heat of fusion of ice as 80 cal g⁻¹ and the specific heat capacity of water as 1 cal g⁻¹ °C⁻¹, the final temperature of the mixture is

  1. 0 °C
  2. 10 °C
  3. 20 °C Correct answer.
  4. 25 °C

Explanation

Melting 10 g of ice needs 10 × 80 = 800 cal, while cooling 50 g of water from 40 °C to 0 °C would release 50 × 1 × 40 = 2000 cal, so all the ice melts and the mixture ends above 0 °C. Let the final temperature be T: 50(40 − T) = 800 + 10T, giving 2000 − 50T = 800 + 10T, so 60T = 1200 and T = 20 °C.

Question 50Heat and Thermal Phenomena (Physics)

A glass vessel filled to the brim with a liquid is gently warmed. The liquid level is seen to fall a little at first and then to rise steadily. The best explanation is that

  1. surface tension of the liquid rises when warmed
  2. the liquid contracts first and then expands
  3. the liquid evaporates quickly and then stops
  4. the vessel warms and expands before the liquid does Correct answer.

Explanation

Heat reaches the glass walls first, so the vessel expands and its internal capacity increases before the liquid inside has warmed appreciably, and the level therefore drops slightly. As the liquid warms, it expands more than the glass because its coefficient of volume expansion is much larger, so the level then rises. The effect shows the difference between real and apparent expansion of a liquid.