9th class Physics, Chapter 4: Turning Effects of Force MCQs

1. A particle is simultaneously acted upon by two forces of 4 and 3 newtons. The net force on the particle is:

1. (A) 1 N
2. (B) between 1 N and 7 N ✓
3. (C) 5 N
4. (D) 7 N

2. A force F is making an angle of 60° with x-axis. Its y-component is equal to:

1. (A) F
2. (B) F sin 60° ✓
3. (C) F cos 60°
4. (D) F tan 60°

3. Moment of force is called:

1. (A) moment arm
2. (B) couple
3. (C) couple arm
4. (D) torque ✓

4. If F₁ and F₂ are the forces acting on a body and τ is the torque produced in it, the body will be completely in equilibrium when:

1. (A) ΣF = 0 and Στ = 0 ✓
2. (B) ΣF = 0 and Στ ≠ 0
3. (C) ΣF ≠ 0 and Στ = 0
4. (D) ΣF ≠ 0 and Στ ≠ 0

5. A shopkeeper sells his articles by a balance having unequal arms of the pans. If he puts the weights in the pan having shorter arm, then the customer:

1. (A) loses ✓
2. (B) gains
3. (C) neither loses nor gains
4. (D) not certain

6. A man walks on a tight rope. He balances himself by holding a bamboo stick horizontally. It is an application of:

1. (A) law of conservation of momentum
2. (B) Newton's second law of motion
3. (C) principle of moments ✓
4. (D) Newton's third law of motion

7. In stable equilibrium, the centre of gravity of the body lies:

1. (A) at the highest position
2. (B) at the lowest position ✓
3. (C) at any position
4. (D) outside the body

8. The centre of mass of a body:

1. (A) lies always inside the body
2. (B) lies always outside the body
3. (C) lies always on the surface of the body
4. (D) may lie within, outside or on the surface ✓

9. A cylinder resting on its circular base is in:

1. (A) stable equilibrium ✓
2. (B) unstable equilibrium
3. (C) neutral equilibrium
4. (D) none of these

10. Centripetal force is given by:

1. (A) rF
2. (B) rF cos θ
3. (C) mv² / r ✓
4. (D) mv / r²

11. Forces which act parallel to one another in the same direction are called:

1. (A) like parallel forces ✓
2. (B) unlike parallel forces
3. (C) couple
4. (D) resultant forces

12. Parallel forces acting in opposite directions are called:

1. (A) like parallel forces
2. (B) rectangular components
3. (C) centripetal forces
4. (D) unlike parallel forces ✓

13. Forces can be added by:

1. (A) subtracting their directions
2. (B) the head-to-tail rule ✓
3. (C) simple arithmetic only
4. (D) multiplying them

14. A force which is equal to the sum of all the forces acting on a body is called:

1. (A) resultant force ✓
2. (B) couple
3. (C) torque
4. (D) centripetal force

15. A body in which the distance between any two points remains the same under the action of a force is called a:

1. (A) fluid
2. (B) point mass
3. (C) rigid body ✓
4. (D) soft body

16. The straight line joining the centres of the circles along which the particles of a rotating body move is the:

1. (A) axis of rotation ✓
2. (B) line of action
3. (C) moment arm
4. (D) tangent

17. The perpendicular distance of the line of action of a force from the axis of rotation is called the:

1. (A) moment arm ✓
2. (B) couple arm
3. (C) torque
4. (D) resultant

18. Door handles are fixed far from the hinges because:

1. (A) a larger moment arm gives larger torque with less force ✓
2. (B) it looks better
3. (C) it reduces friction
4. (D) it increases the weight of the door

19. The moment of a force is defined as the product of the force and:

1. (A) the moment arm ✓
2. (B) the mass
3. (C) the time
4. (D) the velocity

20. The SI unit of torque is:

1. (A) newton
2. (B) joule per second
3. (C) pascal
4. (D) newton metre ✓