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Physics For Class IX (Science Group)
UNIT 4: TURNING EFFECT OF FORCES
Multiple Choice Questions
Section (A) Multiple Choice Questions (MCQs)
Tick mark (✓) the correct answer:1. A pair of unlike parallel forces having different lines of force produce _______.
(a) equilibrium
(b) torque
(c) a couple ✓
(d) unstable equilibrium
2. Head to tail rule can be used to add ______ forces.
(a) two
(b) three
(c) five
(d) any number of ✓
3. A force of 15 N makes an angle of 60° with horizontal. Its vertical component will be:
(a) 15 N
(b) 10 N
(c) 13 N ✓
(d) 7 N
4. A body is in equilibrium when it has:
(a) uniform speed
(b) uniform acceleration
(c) both a and b
(d) zero acceleration ✓
5. A body is in stable equilibrium after slight tilt if its center of gravity:
(a) remains above the point of contact ✓
(b) remains on one side of point of contact
(c) passes over the point of contact
(d) is at lowest position
6. A body is in unstable equilibrium after slight tilt if its center of gravity:
(a) remains on one side of the point of contact
(b) remains above the point of contact ✓
(c) passes over the point of contact
(d) is positioned at its bottom
7. A body is in neutral equilibrium when its center of gravity:
(a) is at the lowest position
(b) remains at same height ✓
(c) is at highest position
(d) is at its base
8. Bunsen burner is made stable by:
(a) increasing its length
(b) increasing its mass
(c) decreasing its base area
(d) increasing its base area ✓
9. A right rope walker carries a long pole to:
(a) increase his weight
(b) raise his centre of gravity
(c) lower his centre of gravity ✓
(d) keep his centre of gravity in fixed position
10. Stability of a racing car is increased by:
(a) increasing its height
(b) raising its centre of gravity
(c) decreasing its width
(d) lowering its centre of gravity ✓
11. The forces that act along opposite directions are called:
(a) parallel forces
(b) like parallel forces
(c) unlike parallel forces ✓
(d) None of these
12. Force has:
(a) only magnitude
(b) only direction
(c) both magnitude & direction ✓
(d) None of these
13. Graphical method is used for addition of:
(a) one-dimensional vector quantities ✓
(b) two-dimensional vector quantities
(c) three-dimensional vector quantities
(d) All of these
14. sin θ = :
(a) base / hypotenuse
(b) perpendicular / hypotenuse ✓
(c) base / perpendicular
(d) perpendicular s/ base
15. perpendicular / base = :
(a) sin θ
(b) cos θ
(c) tan θ ✓
(d) cosec θ
16. The turning effect of force is called:
(a) moment of force
(b) torque
(c) Both 'a' & 'b' ✓
(d) None of these
17. Torque depends upon:
(a) the magnitude of the velocity and fulcrum
(b) the mass & fulcrum
(c) the direction of the force & fulcrum
(d) the magnitude of the force & fulcrum ✓
18. Moment of force about a point is equal to:
(a) 𝜏 = d x F
(b) 𝜏 = F x d ✓
(c) 𝜏 = d . F
(d) 𝜏 = F . d
19. SI unit of the torque or moment of force is:
(a) Newton
(b) Newton per second
(c) Newton-second
(d) Newton-metre ✓
20. The Center of gravity of uniform square or a rectangular sheet is the:
(a) point of intersection of its diagonals ✓
(b) the mid-point on its axis
(c) the point of intersection of its medians
(d) its center
21. The Center of gravity of a uniform triangular sheet is:
(a) point of intersection of its diagonals
(b) the mid-point on its axis
(c) the point of intersection of its medians ✓
(d) its center
22. They form a couple.
(a) two unlike parallel forces of the same magnitude acting along the same line
(b) two unlike parallel forces of the same magnitude not acting along the same line ✓
(c) two like parallel forces of the same magnitude acting along the same line
(d) two like parallel forces of the same magnitude not acting along the same line
23. To form a couple, two forces must be:
(a) equal in magnitude
(b) parallel, but opposite in direction
(c) separated by a distance
(d) All of these ✓
24. A wall hanging, buildings, bridges or any object lying in rest on the ground are some examples of:
(a) dynamic equilibrium
(b) static equilibrium ✓
(c) inertia
(d) acceleration due to gravity
25. A body must satisfy _____ conditions to be in equilibrium.
(a) two ✓
(b) three
(c) four
(d) five
26. According to the first condition for equilibrium:
(a) sum of the all forces acting on a body must be constant
(b) sum of the all forces acting on a body must be equal to zero ✓
(c) sum of all torques acting on a body is constant
(d) sum of all torques acting on a body is zero
27. The following expression represents: F = ma
(a) Newton's first law of motion
(b) Newton's second law of motion ✓
(c) the first condition of equilibrium
(d) the second condition of equilibrium
28. A paratrooper moving down with terminal velocity satisfies:
(a) law of gravitation
(b) Newton's second law of motion
(c) the first condition of equilibrium ✓
(d) the second condition of equilibrium
29. According to the second condition for equilibrium:
(a) sum of the all forces acting on a body must be constant
(b) sum of the all forces acting on a body must be equal to zero
(c) sum of all torques acting on a body is constant
(d) sum of all torques acting on a body is zero ✓
30. States of equilibrium are:
(a) two
(b) three ✓
(c) four
(d) five
31. When a body is slightly displaced and then released it returns to its previous position then the equilibrium will be:
(a) stable equilibrium ✓
(b) unstable equilibrium
(c) neutral equilibrium
(d) None of these
32. If a body is slightly titled and does not return back to its previous position, the body is said to be in:
(a) stable equilibrium
(b) unstable equilibrium ✓
(c) neutral equilibrium
(d) None of these
FILL IN THE BLANKS
- Lines of action of parallel forces are parallel to each other.
- Parallel forces with same direction are called like parallel forces.
- Parallel forces with opposite directions are called unlike parallel forces.
- The sum of the two or more forces is called the resultant of forces.
- The graphical method for addition of forces is called head to tail rule.
- Splitting of a force into two perpendicular components is called resolution of force.
- The perpendicular components of force are Fx =F cosθ, Fy =F sinθ
-
Perpendicular components can be used to determine a force as:
- Turning effect of force is called moment of force or torque.
- The product of the force and the moment arm of the force is equal to the torque.
- The principle of moment states that a body is in equilibrium, if sum of the clockwise moments acting on a body is equal to the sum of the anticlockwise moments acting on the body.
- The Center of mass or Center of gravity is a point where whole weight of the body acts vertically downward.
- Two equal and opposite forces acting along different lines of action form a couple.
- First condition for equilibrium is satisfied if net force acting on a body is zero.
- Second condition for equilibrium is satisfied if sum of clockwise torques acting on a body is equal to the sum of the anticlockwise torques.
- A body is said to be in stable equilibrium if it returns back to previous position after slight tilt.
- A body is to be in neutral equilibrium if it does not return back to previous position but remains in equilibrium at new position after disturbance.
CONCEPT MAP
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