Physics 9 long questions and Answers

Long Questions

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Physics 9 Long Questions and Answers – Chapters 1 to 9

Physics is the study of matter, energy, and the fundamental laws that govern the universe. For 9th-grade students, understanding physics concepts through long-answer questions helps in developing analytical and problem-solving skills. Below are detailed long questions and answers from Chapters 1 to 9 of Physics.

Chapter 1: Physical Quantities and Measurement

Q1: Define physical quantities. Differentiate between base and derived quantities with examples.

Answer:
A physical quantity is a property of a material or system that can be measured and expressed in numerical form.

Types of Physical Quantities:

  1. Base Quantities: These are fundamental physical quantities that are independent of other quantities.

    • Examples: Length (m), Mass (kg), Time (s), Temperature (K).

  2. Derived Quantities: These are obtained by combining base quantities through mathematical operations.

    • Examples: Speed (m/s), Force (N), Work (J).

Chapter 2: Kinematics

Q2: Define kinematics and explain the three equations of motion with derivations.

Answer:
Kinematics is the branch of physics that deals with the motion of objects without considering the causes of motion.

Equations of Motion:

  1. First Equation:  v=u+at

    • Derived from the acceleration formula:  .

  2. Second Equation:    s = ut + 1/2 ​at2

    • Derived using average velocity and total displacement.

  3. Third Equation:  v2 = u2 + 2as

    • Derived by eliminating time tt from the first two equations.

These equations help calculate velocity, acceleration, and displacement in uniformly accelerated motion.

Chapter 3: Dynamics – I

Q3: Explain Newton’s three laws of motion with examples.

Answer:

  1. First Law (Law of Inertia): An object remains at rest or moves in uniform motion unless acted upon by an external force.

    • Example: A stationary car remains at rest until a force is applied.

  2. Second Law (Law of Acceleration): The force acting on an object is equal to the product of its mass and acceleration:

    F=ma

    • Example: A heavier object requires more force to accelerate than a lighter one.

  3. Third Law (Action-Reaction Law): For every action, there is an equal and opposite reaction.

    • Example: A rocket launches upward by pushing gases downward.

Chapter 4: Dynamics – II

Q4: What is momentum? State and explain the law of conservation of momentum.

Answer:
Momentum (p) is the product of mass and velocity of an object:

p=mv

Law of Conservation of Momentum:
The total momentum of an isolated system remains constant before and after a collision, provided no external force acts on it.

Mathematical Representation:

where m1 , m2 are masses and u1 , u2 , v1 ,v2  are initial and final velocities.

Example: When a gun is fired, the bullet moves forward, and the gun recoils backward with equal momentum.

Chapter 5: Pressure and Deformation in Solids

Q5: Define pressure and explain Pascal’s principle with applications.

Answer:
Pressure (P) is the force exerted per unit area:

Pascal’s Principle:
A change in pressure applied to an enclosed fluid is transmitted equally in all directions.

Applications:

  1. Hydraulic Brakes: Used in vehicles to apply equal pressure on all wheels.

  2. Hydraulic Lift: Used in car repair shops to lift vehicles.

  3. Syringes: When pressure is applied, liquid is pushed out uniformly.

Chapter 6: Work and Energy

Q6: Define work and energy. Explain the different types of energy.

Answer:
Work (W) is done when a force causes displacement:

W = Fdcosθ

Energy is the capacity to do work.

Types of Energy:

  1. Kinetic Energy: Energy due to motion:

    KE = 1/2 mv2

  2. Potential Energy: Energy due to position:

    PE = mgh

  3. Thermal Energy: Energy due to heat.

  4. Chemical Energy: Stored in chemical bonds (e.g., food, fuel).

  5. Electrical Energy: Energy carried by electric charges.

Chapter 7: Density and Temperature

Q7: Define density and explain the concept of relative density.

Answer:
Density (ρ) is mass per unit volume:

Relative Density:
The ratio of the density of a substance to the density of water:

Application: Helps determine whether an object will sink or float in water.

Chapter 8: Magnetism

Q8: What are the properties of magnets? Explain the Earth’s magnetic field.

Answer:
Properties of Magnets:

  1. Polarity: Every magnet has a north and south pole.

  2. Attraction and Repulsion: Like poles repel, unlike poles attract.

  3. Magnetic Field: The region around a magnet where magnetic force is exerted.

Earth’s Magnetic Field:

  • Earth behaves like a giant magnet with a magnetic north and south pole.

  • The geomagnetic field protects Earth from solar radiation.

Chapter 9: Nature of Science and Physics

Q9: What is the scientific method? Explain its importance.

Answer:
The scientific method is a systematic process used in scientific investigation.

Steps:

  1. Observation: Identify a phenomenon.

  2. Hypothesis: Formulate a possible explanation.

  3. Experimentation: Conduct experiments to test the hypothesis.

  4. Analysis: Interpret data and draw conclusions.

  5. Theory Development: If validated, the hypothesis becomes a theory.

Importance:

  • Ensures accurate and reliable scientific discoveries.

  • Helps solve real-world problems through logical reasoning.

Conclusion

Understanding physics through long-answer questions helps students grasp fundamental concepts such as motion, forces, energy, magnetism, and scientific methodology. Mastering these topics builds a strong foundation for future studies and real-world applications. 🚀 Happy learning!