9th class Physics, Chapter 3: Dynamics MCQs

1. When we kick a stone, we get hurt. This is due to:

1. (A) inertia
2. (B) velocity
3. (C) momentum
4. (D) reaction ✓

2. An object will continue its motion with constant acceleration until:

1. (A) the resultant force on it begins to decrease ✓
2. (B) the resultant force on it is zero
3. (C) the resultant force on it begins to increase
4. (D) the resultant force is at right angle to its tangential velocity

3. Which of the following is a non-contact force?

1. (A) Friction
2. (B) Air resistance
3. (C) Electrostatic force ✓
4. (D) Tension in the string

4. A ball with initial momentum p hits a solid wall and bounces back with the same velocity. Its momentum p′ after collision will be:

1. (A) p′ = p
2. (B) p′ = -p ✓
3. (C) p′ = 2p
4. (D) p′ = -2p

5. A particle of mass m moving with a velocity v collides with another particle of the same mass at rest. The velocity of the first particle after collision is:

1. (A) v
2. (B) -v
3. (C) 0 ✓
4. (D) -1/2

6. Conservation of linear momentum is equivalent to:

1. (A) Newton's first law of motion
2. (B) Newton's second law of motion
3. (C) Newton's third law of motion ✓
4. (D) None of these

7. An object with a mass of 5 kg moves at constant velocity of 10 m s⁻¹. A constant force then acts for 5 seconds on the object and gives it a velocity of 2 m s⁻¹ in the opposite direction. The force acting on the object is:

1. (A) 5 N
2. (B) -10 N
3. (C) -12 N ✓
4. (D) -15 N

8. A large force acts on an object for a very short interval of time. In this case, it is easy to determine:

1. (A) magnitude of force
2. (B) time interval
3. (C) product of force and time ✓
4. (D) none of these

9. A lubricant is usually introduced between two surfaces to decrease friction. The lubricant:

1. (A) decreases temperature
2. (B) acts as ball bearings
3. (C) prevents direct contact of the surfaces ✓
4. (D) provides rolling friction

10. A force is a:

1. (A) speed
2. (B) distance
3. (C) form of heat only
4. (D) push or a pull ✓

11. Dynamics is concerned with:

1. (A) the temperature of bodies
2. (B) the size of bodies
3. (C) the forces that produce change in the motion of bodies ✓
4. (D) motion without forces

12. A force exerted by one object on another at the point of contact is called a:

1. (A) field force
2. (B) contact force ✓
3. (C) non-contact force
4. (D) nuclear force

13. The force that resists motion when the surface of one object is in contact with the surface of another is:

1. (A) thrust
2. (B) tension
3. (C) gravity
4. (D) friction ✓

14. The resistant force caused by the motion of a body through a fluid is called:

1. (A) drag ✓
2. (B) thrust
3. (C) normal force
4. (D) tension

15. The upward force exerted by a liquid on an object immersed in it is called:

1. (A) tension
2. (B) thrust ✓
3. (C) drag
4. (D) friction

16. The force of reaction exerted by a surface on an object lying on it, acting perpendicular to the surface, is the:

1. (A) tension force
2. (B) elastic force
3. (C) drag force
4. (D) normal force ✓

17. The force experienced by a rope when a person or load pulls it is the:

1. (A) tension force ✓
2. (B) normal force
3. (C) thrust
4. (D) elastic force

18. Rubber bands, springs and a trampoline show the:

1. (A) drag force
2. (B) elastic force ✓
3. (C) magnetic force
4. (D) nuclear force

19. Non-contact forces are also called:

1. (A) normal forces
2. (B) field forces ✓
3. (C) applied forces
4. (D) tension forces

20. The value of the constant of gravitation G is:

1. (A) 6.67 × 10⁻⁹ N m kg⁻¹
2. (B) 6.67 × 10⁻¹¹ N m² kg⁻² ✓
3. (C) 6.67 × 10¹¹ N m² kg⁻²
4. (D) 9.8 N m² kg⁻²