Class 11 Physics Important Questions with Solutions

Class 11 Physics Important Questions provide chapter-wise practice across mechanics, properties of matter, heat, thermodynamics, oscillations and waves. These questions follow the current CBSE and NCERT Class 11 Physics course and include conceptual, numerical and derivation-based practice.

Class 11 Physics introduces students to measurement, motion, forces, energy, gravitation, properties of matter, thermodynamics and waves. These concepts also form the base for several topics studied in Class 12.

The Class 11 Physics Important Questions given below include direct theory questions, formula-based numericals and longer applications. Students can use them for school examinations, periodic tests and chapter-wise revision.

Key Takeaways

• Class 11 Physics currently contains 14 chapters.
• The course begins with Units and Measurements and ends with Waves.
• Mechanics forms a large part of the syllabus.
• Numerical questions require correct formulas, substitutions and SI units.
• Derivations should include every important step.
• Diagrams and free-body diagrams improve many Physics answers.

CBSE Class 11 Physics Chapter-Wise Important Questions 

Important Class 11 Physics Formulas

Access Class 11 Physics Important Questions in 30 Minutes

• First 10 minutes: Revise units, kinematics, laws of motion, work, energy and gravitation.
• Next 10 minutes: Review rotational motion, solids, fluids, thermal properties and thermodynamics.
• Final 10 minutes: Practise kinetic theory, oscillations and waves.

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Very Short Answer Questions for Class 11 Physics

Q1. What is a physical quantity?

Answer: A physical quantity is a measurable property expressed using a numerical value and a unit.

Q2. What is the SI unit of force?

Answer: The SI unit of force is newton, represented by N.

Q3. What is the difference between distance and displacement?

Answer: Distance is the total path travelled by an object. Displacement is the shortest directed distance between its initial and final positions.

Q4. What is a scalar quantity?

Answer: A scalar quantity has magnitude but no direction. Mass, time and temperature are examples.

Q5. What is a vector quantity?

Answer: A vector quantity has both magnitude and direction. Velocity, force and momentum are examples.

Q6. State Newton’s first law of motion.

Answer: A body remains at rest or in uniform straight-line motion unless an external unbalanced force acts on it.

Q7. Define linear momentum.

Answer: Linear momentum is the product of mass and velocity.

p = mv

Q8. What is inertia?

Answer: Inertia is the tendency of a body to resist any change in its state of rest or uniform motion.

Q9. Define work done by a constant force.

Answer: Work done is the product of force, displacement and the cosine of the angle between them.

W = Fs cos θ

Q10. When is work done equal to zero?

Answer: Work is zero when displacement is zero or the force is perpendicular to displacement.

Q11. State the work-energy theorem.

Answer: The net work done on a body equals the change in its kinetic energy.

Wnet = ΔKE

Q12. Define torque.

Answer: Torque is the turning effect of a force about an axis.

τ = rF sin θ

Q13. What is the centre of mass?

Answer: The centre of mass is the point at which the whole mass of a system may be considered concentrated for translational motion.

Q14. State Newton’s law of gravitation.

Answer: Every two masses attract each other with a force directly proportional to their masses and inversely proportional to the square of their separation.

F = Gm₁m₂/r²

Q15. Define stress.

Answer: Stress is the restoring force per unit area developed inside a deformed body.

Stress = Force/Area

Q16. Define strain.

Answer: Strain is the ratio of change in dimension to the original dimension. It has no unit.

Q17. State Pascal’s law.

Answer: Pressure applied to an enclosed fluid is transmitted equally and undiminished in all directions.

Q18. What is surface tension?

Answer: Surface tension is the force acting per unit length on an imaginary line drawn on the free surface of a liquid.

Q19. State the zeroth law of thermodynamics.

Answer: If two systems are separately in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

Q20. What is simple harmonic motion?

Answer: Simple harmonic motion is periodic motion in which the restoring force is directly proportional and opposite to displacement.

F = −kx

Short Answer and Numerical Questions for Class 11 Physics

Q21. A car travels 60 km in 2 hours and then 40 km in 1 hour. Find its average speed.

Solution:

Total distance:

Distance = 60 + 40

Distance = 100 km

Total time:

Time = 2 + 1

Time = 3 hours

Average speed:

Average speed = Total distance/Total time

Average speed = 100/3

Average speed = 33.3 km/h

Q22. A body starts from rest and accelerates uniformly at 2 m/s² for 5 seconds. Find its final velocity.

Solution:

Given:

u = 0

a = 2 m/s²

t = 5 s

Using:

v = u + at

v = 0 + 2(5)

v = 10 m/s

Q23. Find the displacement of the body in Q22.

Solution:

Using:

s = ut + 1/2 at²

s = 0(5) + 1/2(2)(5²)

s = 25 m

Q24. A projectile is thrown with a speed of 20 m/s at an angle of 30°. Find its horizontal component of velocity.

Solution:

Horizontal component:

ux = u cos θ

ux = 20 cos 30°

ux = 20(√3/2)

ux = 10√3 m/s

Q25. A force of 10 N acts on a body of mass 2 kg. Find its acceleration.

Solution:

F = ma

Therefore:

a = F/m

a = 10/2

a = 5 m/s²

Q26. A 5 kg body moves with a speed of 4 m/s. Find its momentum.

Solution:

p = mv

p = 5 × 4

p = 20 kg m/s

Q27. Find the kinetic energy of a 2 kg body moving at 6 m/s.

Solution:

KE = 1/2 mv²

KE = 1/2(2)(6²)

KE = 36 J

Q28. A force of 20 N moves an object through 5 m in the direction of the force. Find the work done.

Solution:

W = Fs cos θ

Here:

θ = 0°

W = 20 × 5 × cos 0°

W = 100 J

Q29. A machine does 600 J of work in 3 seconds. Find its power.

Solution:

Power = Work/Time

P = 600/3

P = 200 W

Q30. A force of 50 N acts at a perpendicular distance of 0.2 m from an axis. Find the torque.

Solution:

τ = rF

τ = 0.2 × 50

τ = 10 N m

Q31. Find the gravitational force between masses 2 kg and 3 kg separated by 2 m.

Solution:

F = Gm₁m₂/r²

F = G(2)(3)/(2²)

F = 6G/4

F = 1.5G N

Using G = 6.67 × 10⁻¹¹ N m²/kg²:

F = 1.0005 × 10⁻¹⁰ N

Q32. A body of mass 4 kg is raised through a height of 5 m. Find its potential energy. Take g = 9.8 m/s².

Solution:

PE = mgh

PE = 4 × 9.8 × 5

PE = 196 J

Q33. A force of 100 N acts on an area of 0.5 m². Find the pressure.

Solution:

P = F/A

P = 100/0.5

P = 200 Pa

Q34. A substance has a mass of 600 g and volume of 200 cm³. Find its density.

Solution:

Density = Mass/Volume

Density = 600/200

Density = 3 g/cm³

Q35. Calculate the heat needed to raise the temperature of 2 kg of water by 5°C. Take c = 4200 J/kg°C.

Solution:

Q = mcΔT

Q = 2 × 4200 × 5

Q = 42,000 J

Q36. A gas absorbs 500 J of heat and performs 200 J of work. Find the change in internal energy.

Solution:

Using the first law:

ΔQ = ΔU + ΔW

Therefore:

ΔU = ΔQ − ΔW

ΔU = 500 − 200

ΔU = 300 J

Q37. Find the time period of a simple pendulum of length 1 m. Take g = 9.8 m/s².

Solution:

T = 2π√(l/g)

T = 2π√(1/9.8)

T ≈ 2.01 s

Q38. A wave has frequency 50 Hz and wavelength 2 m. Find its speed.

Solution:

v = fλ

v = 50 × 2

v = 100 m/s

Long Answer and Derivation Questions for Class 11 Physics

Q39. Derive the equation v = u + at.

Solution:

Acceleration is defined as the rate of change of velocity.

a = (v − u)/t

Multiplying both sides by t:

at = v − u

Therefore:

v = u + at

Q40. Derive the equation s = ut + 1/2 at².

Solution:

For uniformly accelerated motion:

Average velocity = (u + v)/2

Displacement:

s = Average velocity × Time

s = [(u + v)/2]t

Using:

v = u + at

Substitute v:

s = [u + u + at]t/2

s = [2u + at]t/2

Therefore:

s = ut + 1/2 at²

Q41. Derive the relation v² = u² + 2as.

Solution:

Use:

v = u + at

Therefore:

t = (v − u)/a

Also:

s = [(u + v)/2]t

Substitute t:

s = [(u + v)/2][(v − u)/a]

s = (v² − u²)/(2a)

Therefore:

2as = v² − u²

Hence:

v² = u² + 2as

Q42. Prove the law of conservation of linear momentum for two interacting bodies.

Solution:

Consider two bodies of masses m₁ and m₂.

Let their initial velocities be u₁ and u₂. After interaction, their velocities become v₁ and v₂.

According to Newton’s third law:

F₁₂ = −F₂₁

Using force as the rate of change of momentum:

m₁(v₁ − u₁)/t = −m₂(v₂ − u₂)/t

Therefore:

m₁v₁ − m₁u₁ = −m₂v₂ + m₂u₂

Rearranging:

m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

Thus, total initial momentum equals total final momentum.

Q43. Derive the expression for kinetic energy.

Solution:

Let a force F move a body of mass m through displacement s.

Work done:

W = Fs

Using:

F = ma

Therefore:

W = mas

From:

v² = u² + 2as

We get:

as = (v² − u²)/2

Therefore:

W = m(v² − u²)/2

W = 1/2 mv² − 1/2 mu²

Hence, work done equals the change in kinetic energy.

For a body starting from rest:

KE = 1/2 mv²

Q44. Derive the expression for acceleration due to gravity at Earth’s surface.

Solution:

The gravitational force on a body of mass m at Earth’s surface is:

F = GMm/R²

The weight of the body is:

F = mg

Equating:

mg = GMm/R²

Cancelling m:

g = GM/R²

Here, M is Earth’s mass and R is Earth’s radius.

Q45. Explain Bernoulli’s principle.

Answer: Bernoulli’s principle states that the total energy per unit volume of an ideal fluid remains constant along a streamline.

P + 1/2 ρv² + ρgh = Constant

An increase in fluid speed causes a decrease in pressure when height remains unchanged. The principle is applied in atomisers, aircraft wings and venturimeters.

Q46. State and explain the first law of thermodynamics.

Answer: The first law of thermodynamics is a statement of conservation of energy for a thermodynamic system.

ΔQ = ΔU + ΔW

Heat supplied to a system is used to increase its internal energy and perform external work.

Here:

• ΔQ is the heat supplied
• ΔU is the change in internal energy
• ΔW is the work done by the system

Q47. Derive the time period of a mass attached to a spring.

Solution:

For a spring:

F = −kx

According to Newton’s second law:

F = ma

Therefore:

ma = −kx

a = −(k/m)x

For SHM:

a = −ω²x

Comparing:

ω² = k/m

ω = √(k/m)

Time period:

T = 2π/ω

Therefore:

T = 2π√(m/k)

Q48. Explain the formation of standing waves.

Answer: Standing waves form when two waves of the same frequency, wavelength and amplitude travel in opposite directions and interfere.

The resulting pattern has fixed points called nodes, where displacement remains zero. Antinodes are points of maximum displacement.

The distance between two consecutive nodes is:

λ/2

The distance between a node and the nearest antinode is:

λ/4

Practice Questions for Class 11 Physics

1. Convert 72 km/h into m/s.
2. Find the percentage error when a measured length is 5.0 ± 0.1 cm.
3. A body moving at 10 m/s stops in 5 seconds. Find its acceleration.
4. A projectile is launched at 20 m/s at 45°. Find its maximum height.
5. Draw the free-body diagram of a block resting on a rough inclined plane.
6. A 4 kg body moving at 5 m/s collides with a stationary 6 kg body. Find their common velocity if they stick together.
7. Find the work done in stretching a spring of force constant 200 N/m by 0.1 m.
8. Find the moment of inertia of two point masses of 2 kg each placed 0.5 m from an axis.
9. Calculate the value of g at a height equal to Earth’s radius.
10. A wire of length 2 m extends by 1 mm under a force. Calculate its strain.
11. Explain why a needle floats on water when placed carefully.
12. Find the excess pressure inside a soap bubble of radius r.
13. Distinguish between heat and temperature.
14. Explain an isothermal process using a pressure-volume graph.
15. Derive the relation between pressure and kinetic energy density of a gas.
16. Find the total energy of a particle performing SHM.
17. Explain resonance with one daily-life example.
18. Distinguish between progressive and standing waves.