Class 9 Physics MCQs: Dynamics - I

MCQs (sample)

Showing 25 questions from this chapter. For a full timed test, use “Start online test”.

1. 1. What is the formula for momentum?

   • p = mv
   • p = m/v
   • p = m + v
   • p = mv^2
   Answer & explanation

   Correct: p = mv

   Momentum is defined as the product of an object's mass and its velocity, mathematically expressed as p = mv.

2. 2. What is the definition of force?

   • A vector quantity that changes or tends to change the state of a body
   • A scalar quantity that remains constant
   • A force that acts only at a distance
   • A force that can only change speed
   Answer & explanation

   Correct: A vector quantity that changes or tends to change the state of a body

   Force is defined as a vector quantity that changes or tends to change the state of a body, affecting its motion.

3. 3. What is mass defined as?

   • The amount of matter an object contains
   • The gravitational force acting on an object
   • A measure of distance
   • The weight of an object
   Answer & explanation

   Correct: The amount of matter an object contains

   Mass is defined as the amount of matter an object contains.

4. 4. What is the term for the region around a massive object where gravitational force is operative?

   • Gravitational field
   • Magnetic field
   • Electric field
   • Force field
   Answer & explanation

   Correct: Gravitational field

   The region around a massive object where gravitational force is operative is termed a gravitational field.

5. 5. What does Newton's First Law of Motion state about an object with no net external force acting on it?

   • It will maintain its state of rest or uniform motion.
   • It will always change its state of motion.
   • It will accelerate continuously.
   • It will eventually stop moving.
   Answer & explanation

   Correct: It will maintain its state of rest or uniform motion.

   According to Newton's First Law, an object will maintain its state of rest or uniform motion if no net external force acts on it.

6. 6. What is the SI unit of momentum?

   • kilogram-meter per second (kgm/s)
   • newton (N)
   • kilogram (kg)
   • meter per second squared (m/s²)
   Answer & explanation

   Correct: kilogram-meter per second (kgm/s)

   The SI unit of momentum is kilogram-meter per second (kgm/s) or newton-second (Ns).

7. 7. What are the two broad classifications of forces?

   • Friction and tension
   • Contact and non-contact forces
   • Balanced and unbalanced forces
   • Mass and weight
   Answer & explanation

   Correct: Contact and non-contact forces

   Forces are broadly classified as contact forces and non-contact forces.

8. 8. What does weight refer to?

   • The amount of matter in an object
   • The measure of inertia of an object
   • The gravitational force acting on a mass or object
   • The volume of an object
   Answer & explanation

   Correct: The gravitational force acting on a mass or object

   Weight refers to the gravitational force acting on a mass or object.

9. 9. What does the symbol 'g' represent in the context of gravitational fields?

   • Gravitational field strength
   • Mass of an object
   • Force applied
   • Acceleration of an object
   Answer & explanation

   Correct: Gravitational field strength

   'g' represents the gravitational field strength, equal to the magnitude of the gravitational force exerted on a unit mass.

10. 10. What is the natural tendency of an object described in Newton's First Law called?

    • Inertia
    • Momentum
    • Force
    • Acceleration
    Answer & explanation

    Correct: Inertia

    The term describing the natural tendency of an object to remain at rest or in uniform motion is inertia.

11. 11. What does the direction of momentum point towards?

    • Same direction as mass
    • Same direction as velocity
    • Opposite direction to velocity
    • Any random direction
    Answer & explanation

    Correct: Same direction as velocity

    Momentum is a vector quantity and points in the same direction as the velocity.

12. 12. Which of the following is a contact force?

    • Gravitational force
    • Magnetic force
    • Friction
    • Electrostatic force
    Answer & explanation

    Correct: Friction

    Friction is an example of a contact force that acts between two objects in physical contact.

13. 13. Which equation relates weight and mass?

    • W = m/g
    • W = mg
    • W = mass/g
    • W = g/m
    Answer & explanation

    Correct: W = mg

    The equation that relates weight and mass is W = mg.

14. 14. How is gravitational field strength (g) mathematically defined?

    • g = F/m
    • g = m/F
    • g = F * m
    • g = m + F
    Answer & explanation

    Correct: g = F/m

    Gravitational field strength is defined mathematically as g = F/m, where F is the force and m is the mass.

15. 15. According to Newton's Second Law, what is the relationship between force, mass, and acceleration?

    • Force is directly proportional to mass and acceleration.
    • Acceleration is inversely proportional to mass and directly proportional to force.
    • Force is inversely proportional to mass.
    • Mass is directly proportional to acceleration.
    Answer & explanation

    Correct: Acceleration is inversely proportional to mass and directly proportional to force.

    Newton's Second Law states that acceleration is directly proportional to the net force and inversely proportional to the mass of the object.

16. 16. According to the content, what happens when there is a sudden change in momentum?

    • Force is large
    • Force is zero
    • Force is small
    • Force is constant
    Answer & explanation

    Correct: Force is large

    For sudden change in momentum, the force acting on the body must be large.

17. 17. What type of forces act at a distance without physical contact?

    • Contact forces
    • Electromagnetic forces
    • Non-contact forces
    • Balanced forces
    Answer & explanation

    Correct: Non-contact forces

    Non-contact forces act at a distance without physical contact between bodies.

18. 18. How does mass change when moving from Earth to the Moon?

    • It decreases
    • It increases
    • It remains the same
    • It is undefined
    Answer & explanation

    Correct: It remains the same

    Mass remains the same regardless of location; it does not change when moving from Earth to the Moon.

19. 19. In which unit is gravitational field strength measured in the SI system?

    • Newton per kilogram (N/kg)
    • Kilogram per meter (kg/m)
    • Meter per second squared (m/s²)
    • Joule per kilogram (J/kg)
    Answer & explanation

    Correct: Newton per kilogram (N/kg)

    Gravitational field strength is measured in newton per kilogram (N/kg) in the SI system.

20. 20. What is the mathematical expression of Newton's Second Law?

    • F_net = mv
    • F_net = ma
    • F_net = m/v
    • F_net = ma^2
    Answer & explanation

    Correct: F_net = ma

    The correct mathematical expression of Newton's Second Law of Motion is F_net = ma.

21. 21. What is impulse defined as?

    • Force multiplied by time interval
    • Mass times acceleration
    • Velocity times distance
    • Energy divided by time
    Answer & explanation

    Correct: Force multiplied by time interval

    Impulse is the product of the force exerted on an object and the time interval over which the force acts.

22. 22. Which force keeps protons tightly packed in the nucleus?

    • Electromagnetic force
    • Weak nuclear force
    • Gravitational force
    • Strong nuclear force
    Answer & explanation

    Correct: Strong nuclear force

    The strong nuclear force is responsible for keeping the positively charged protons tightly packed in the nucleus.

23. 23. What would happen to weight when moving to the Moon?

    • It would double
    • It would increase by 1/6
    • It would be reduced roughly by 5/6
    • It would remain constant
    Answer & explanation

    Correct: It would be reduced roughly by 5/6

    Weight would be reduced roughly by 5/6 when moving to the Moon.

24. 24. What direction does the gravitational field strength vector point?

    • Upward
    • Downward
    • Towards the center of the Earth
    • Toward the sun
    Answer & explanation

    Correct: Towards the center of the Earth

    The gravitational field strength vector points toward the center of the Earth.

25. 25. What happens when one object exerts a force on a second object according to Newton's Third Law?

    • The first object does not move.
    • The second object exerts an equal and opposite force on the first object.
    • The forces cancel each other out.
    • Only one of the objects experiences the force.
    Answer & explanation

    Correct: The second object exerts an equal and opposite force on the first object.

    Newton's Third Law states that an equal and opposite force is exerted by the second object back on the first object.