Class 9th Science - Force and Laws of Motion (JKBOSE) Practice Test 100 MCQs

Class 9th Science - Force and Laws of Motion (JKBOSE) - 100 MCQ Practice Test

Class 9th Science - Force and Laws of Motion (JKBOSE) Practice Test

Targeted 100 MCQ Practice Module focusing on: Force & Its Effects, Newton's First Law & Inertia, Momentum & Newton's Second Law, Newton's Third Law, and Conservation of Momentum.

Select your answers and click Submit Assessment Answers at the bottom to calculate your total score and review explanations.

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SECTION I: Force and Its Effects [Questions 1 to 20]
1. Force is best defined as:
Explanation: Force is simply defined as a push or a pull that an object exerts on another object.
2. What is the SI unit of force?
Explanation: The SI unit of force is the Newton (N), named after Sir Isaac Newton.
3. A force applied on an object can do which of the following?
Explanation: A force can change the speed, direction of motion, and shape/size of an object depending on how it is applied.
4. When two or more forces acting on an object produce no change in its state of rest or motion, the forces are called:
Explanation: When the resultant (net) of all forces acting on a body is zero, the forces are said to be balanced.
5. A force which changes or tends to change the state of rest or of uniform motion of a body is called:
Explanation: An unbalanced (net) force causes a body to accelerate, changing its state of rest or uniform motion.
6. In a tug of war, if both teams pull with exactly equal force in opposite directions, the rope:
Explanation: Equal and opposite forces from both teams cancel out, giving zero net (balanced) force, so the rope stays at rest.
7. Force is a __________ quantity because it has both magnitude and direction.
Explanation: Since force has both magnitude and a specific direction of action, it is classified as a vector quantity.
8. One Newton of force is defined as the force which produces an acceleration of:
Explanation: By definition, 1 Newton is the force required to produce an acceleration of 1 m/s² in a body of mass 1 kg (1 N = 1 kg × 1 m/s²).
9. Kneading dough to change its shape is an example of force causing:
Explanation: Applying force by kneading deforms the dough, demonstrating that force can alter the shape of a body.
10. Friction is an example of which category of force?
Explanation: Friction arises due to actual physical contact between two surfaces, so it is classified as a contact force.
11. Forces are broadly classified into two categories on the basis of contact. These are:
Explanation: Based on whether physical contact is involved, forces are classified as Contact forces (muscular, frictional) and Non-contact forces (gravitational, magnetic, electrostatic).
12. The force exerted by our muscles while lifting or pushing an object is called:
Explanation: Muscular force is the contact force generated by the contraction and relaxation of muscles in living beings.
13. The force which attracts a falling apple towards the Earth without any physical contact is called:
Explanation: Gravitational force is a non-contact force that pulls objects towards the centre of the Earth without touching them.
14. A book lying at rest on a table experiences forces that are:
Explanation: Gravity pulling the book down is exactly balanced by the normal reaction of the table pushing it up, giving zero net force.
15. When an unbalanced (net) force acts on a body, the body will:
Explanation: An unbalanced force produces acceleration in the object in the direction in which the net force acts.
16. A heavy box lying on the floor does not move when pushed gently because the applied force is:
Explanation: Friction between the box and floor opposes the applied push; as long as it equals the applied force, the box remains stationary (balanced forces).
17. In the CGS system, the unit of force is the:
Explanation: The CGS unit of force is the dyne, defined as the force needed to accelerate a 1-gram mass at 1 cm/s².
18. The relationship between Newton and dyne is:
Explanation: Since 1 kg = 1000 g and 1 m = 100 cm, converting units gives 1 N = 1 kg·m/s² = 10⁵ g·cm/s² = 10⁵ dyne.
19. Two forces of equal magnitude acting on a body in opposite directions along the same line will result in a net force of:
Explanation: Since the forces are equal and opposite, they cancel each other out along the line of action, resulting in a net force of zero.
20. A diagram used to represent all the forces acting on an isolated body is called:
Explanation: A free body diagram isolates a body and shows all forces acting on it with arrows, helping analyse balanced/unbalanced conditions.
SECTION II: Newton's First Law of Motion & Inertia [Questions 21 to 40]
21. According to Newton's First Law of Motion, an object remains in its state of rest or uniform motion in a straight line unless:
Explanation: Newton's First Law states a body continues in its state of rest or of uniform motion unless compelled by an external unbalanced force to change that state.
22. Newton's First Law of Motion is also popularly known as the:
Explanation: Because it describes the natural tendency of bodies to resist a change in their state of motion, the First Law is called the Law of Inertia.
23. Inertia of a body may be defined as its:
Explanation: Inertia is the natural property of matter due to which a body resists any change in its existing state of rest or uniform motion.
24. The inertia of a body is directly related to its:
Explanation: Mass is a quantitative measure of inertia — the greater the mass of a body, the greater its inertia.
25. Between a fully loaded truck and an empty auto-rickshaw, which has greater inertia?
Explanation: Since inertia increases with mass, the heavier, fully loaded truck has far greater inertia than the lighter auto-rickshaw.
26. When a bus suddenly starts moving, standing passengers tend to fall backward. This happens due to:
Explanation: The passenger's body was at rest; when the bus suddenly moves forward, the body's lower part moves with the bus but the upper body, due to inertia of rest, tends to stay behind, causing a backward fall.
27. When a running bus suddenly stops, standing passengers tend to fall forward due to:
Explanation: The passenger's body was in motion along with the bus; when the bus stops suddenly, the body tends to continue moving forward due to inertia of motion.
28. Dust particles come out of a carpet when it is beaten with a stick. This is an example of:
Explanation: When the carpet is beaten, it suddenly moves, but the dust particles, due to inertia of rest, tend to remain at rest and hence separate from the carpet.
29. In the classic "magic tablecloth trick," the cloth is pulled quickly and the dishes on it remain in place. This illustrates:
Explanation: Since the cloth is pulled very quickly, the short time of contact means very little force is transferred to the dishes, which stay at rest due to inertia.
30. A person jumping out of a moving bus tends to fall forward upon landing because of:
Explanation: His body was moving along with the bus; upon landing, his feet stop suddenly while the upper body continues moving forward due to inertia of motion, causing a forward fall.
31. Inertia is generally classified into how many types?
Explanation: Inertia is classified into three types: inertia of rest, inertia of motion, and inertia of direction.
32. Mud flying off tangentially from a rapidly spinning bicycle tyre illustrates:
Explanation: The mud tends to continue moving in the straight-line tangential direction it had at the moment of release, illustrating inertia of direction.
33. Which scientist first introduced the concept of inertia before Newton formally stated the First Law?
Explanation: Galileo Galilei studied the motion of objects and laid the groundwork for the concept of inertia, which Newton later formalized as his First Law.
34. Newton's First Law essentially defines which physical quantity?
Explanation: The First Law gives a qualitative definition of force as that external agency which is required to change the state of rest or uniform motion of a body.
35. Seat belts in cars are designed to protect passengers primarily by counteracting their:
Explanation: During sudden braking, a passenger's body tends to keep moving forward due to inertia of motion; the seat belt restrains this and prevents injury.
36. In the classic experiment where a coin placed on a cardboard over the mouth of a glass falls straight into the glass when the card is flicked away, this demonstrates:
Explanation: The coin, being at rest, tends to remain at rest due to inertia even as the card is quickly flicked away, so gravity then pulls it straight down into the glass.
37. A heavier object is generally harder to push into motion than a lighter one because the heavier object has:
Explanation: Since inertia depends on mass, a heavier object resists a change in its state of rest more strongly, making it harder to set into motion.
38. Mass can be regarded as a numerical measure of a body's:
Explanation: Mass quantifies how much a body resists a change in motion, making it the standard measure of inertia.
39. What is the SI unit of mass?
Explanation: The SI unit of mass is the kilogram (kg).
40. Which of the following statements about mass is correct?
Explanation: Mass is a scalar quantity that measures the amount of matter in a body and remains the same regardless of location, unlike weight.
SECTION III: Momentum & Newton's Second Law of Motion [Questions 41 to 60]
41. The momentum of a moving body is defined as the product of its:
Explanation: Momentum (p) is defined as p = mv, the product of a body's mass and its velocity.
42. What is the SI unit of momentum?
Explanation: Since momentum = mass × velocity, its SI unit is kg m/s, which is equivalent to Newton-second (Ns).
43. Momentum is classified as a __________ quantity.
Explanation: Since velocity is a vector and mass is a positive scalar, momentum (mass × velocity) always acts in the direction of velocity, making it a vector quantity.
44. Newton's Second Law of Motion states that the rate of change of momentum of a body is:
Explanation: Newton's Second Law states that the rate of change of momentum of an object is directly proportional to the applied unbalanced force and takes place in the direction of the force.
45. Newton's Second Law can be mathematically expressed for constant mass as:
Explanation: For a body of constant mass, the second law reduces to F = ma, force equals mass times acceleration.
46. From Newton's Second Law, 1 Newton of force is equivalent to:
Explanation: Since F = ma, 1 N is defined as the force that gives a mass of 1 kg an acceleration of 1 m/s², i.e., 1 N = 1 kg·m/s².
47. A force of 20 N acts on a body of mass 4 kg. What is the acceleration produced?
Explanation: Using F = ma, a = F/m = 20 N / 4 kg = 5 m/s².
48. Impulse of a force is defined as the product of:
Explanation: Impulse = F × t, and it is also equal to the total change in momentum produced by the force.
49. Since impulse equals change in momentum, its SI unit can also be expressed as:
Explanation: As Impulse = Δ(momentum), it shares the same unit as momentum: kg m/s, equivalently written as Newton-second (Ns).
50. A cricketer moves his hands backward while catching a fast-moving ball in order to:
Explanation: Since impulse (change in momentum) is fixed, increasing the time of catching reduces the force experienced (F = Δp/Δt), protecting the hands.
51. High jump athletes land on cushioned or sandy pits mainly to:
Explanation: A soft landing surface increases the stopping time, lowering the average force experienced by the body for the same change in momentum.
52. Airbags in cars protect passengers during a collision by:
Explanation: Airbags cushion the impact, extending the time taken for the passenger's momentum to become zero, which reduces the force experienced.
53. If the mass of a body is doubled while the acceleration produced remains the same, the force required will:
Explanation: Since F = ma, if mass doubles and acceleration stays constant, the required force also doubles proportionally.
54. If the velocity of a moving body is doubled while its mass stays constant, its momentum will:
Explanation: Since p = mv, doubling velocity while mass remains constant results in the momentum also being doubled.
55. For a body of constant mass, a greater applied force will produce:
Explanation: As per F = ma, acceleration is directly proportional to the applied force when mass remains constant.
56. A force acting on a body of mass 2 kg produces an acceleration of 3 m/s². What is the magnitude of the force?
Explanation: F = ma = 2 kg × 3 m/s² = 6 N.
57. For a given force, if it acts on a body for a longer duration of time, the resulting change in momentum will be:
Explanation: Since Impulse = F × t = change in momentum, a longer application time for the same force produces a greater total change in momentum.
58. Which of Newton's laws is generally regarded as the real/fundamental law of motion, since the other two laws can be derived as special cases from it?
Explanation: The Second Law (F = dp/dt) is considered the fundamental law since the First Law is its special case when F = 0, and the Third Law can also be shown consistent with it via conservation of momentum.
59. Newton's First Law of Motion can be treated as a special case of the Second Law when:
Explanation: When F = 0 in F = ma, acceleration is also zero, meaning the body continues at constant velocity (or remains at rest) — exactly what the First Law states.
60. According to Newton's Second Law, acceleration produced in a body is:
Explanation: From a = F/m, acceleration increases with greater force but decreases with greater mass — direct proportionality with F, inverse with m.
SECTION IV: Newton's Third Law of Motion [Questions 61 to 80]
61. Newton's Third Law of Motion states that:
Explanation: Newton's Third Law states that for every action, there is an equal and opposite reaction, and these forces act on two different bodies.
62. Action and reaction forces described by Newton's Third Law always act on:
Explanation: Action and reaction always act on two different bodies, which is why they do not cancel each other out despite being equal and opposite.
63. Why don't action-reaction force pairs cancel each other and produce zero net effect on a system?
Explanation: Forces cancel only when acting on the same body; since action and reaction act on different bodies, each body experiences a net force and can accelerate.
64. While walking, a person pushes the ground backward with their foot. According to Newton's Third Law, the ground:
Explanation: The backward push (action) on the ground is met with an equal forward reaction from the ground on the foot, propelling the person forward.
65. A swimmer pushes water backward with their hands and legs while swimming. The forward motion of the swimmer results from:
Explanation: By Newton's Third Law, pushing water backward (action) results in water pushing the swimmer forward (equal, opposite reaction).
66. A rocket is propelled forward into space by:
Explanation: Rockets expel exhaust gases downward/backward at high velocity; the reaction of this ejection propels the rocket forward, working even in the vacuum of space.
67. When a bullet is fired from a gun, the gun moves backward. This backward movement of the gun is called:
Explanation: The backward jerk experienced by a gun on firing a bullet is called recoil, occurring due to Newton's Third Law (and conservation of momentum).
68. The recoil of a gun when a bullet is fired is best explained by:
Explanation: The forward force on the bullet (action) causes an equal and opposite backward force on the gun (reaction), consistent with conservation of total momentum of the system.
69. A person rowing a boat pushes the oars against the water backward, and the boat moves forward. This is an application of:
Explanation: Pushing water backward with oars (action) results in an equal, opposite reaction force from the water pushing the boat forward.
70. A book resting on a table exerts a downward force (its weight) on the table. The table exerts an equal and opposite upward force on the book known as the:
Explanation: This upward reaction force perpendicular to the surface is called the normal reaction, and it balances the book's weight per Newton's Third Law.
71. A person standing in a stationary boat jumps forward onto the shore. As a result, the boat:
Explanation: As the person pushes against the boat to jump forward (action), the boat experiences an equal and opposite reactive push, moving it backward.
72. According to Newton's Third Law, action and reaction forces act:
Explanation: Action and reaction forces always occur simultaneously — neither one exists before the other.
73. Action and reaction forces in a Newton's Third Law pair are always:
Explanation: By definition of the Third Law, action and reaction forces are always equal in magnitude but act in opposite directions.
74. Why do action-reaction forces not produce equilibrium (cancel out) on the system as a whole?
Explanation: Equilibrium requires forces acting on the same body to cancel; since action and reaction act on different bodies, each body still responds to the force acting on it.
75. In an action-reaction pair, which force can correctly be labelled as "action" and which as "reaction"?
Explanation: The labelling of action and reaction is arbitrary; either of the two equal and opposite forces may be called the "action" with the other as "reaction".
76. A horse pulls a cart forward. According to Newton's Third Law, the reaction to this action is the:
Explanation: As the horse pulls the cart forward (action), the cart exerts an equal and opposite backward pull on the horse (reaction); the horse still moves forward due to the ground's reaction on its legs.
77. When a gun fires a bullet, the recoil velocity of the gun is much smaller than the velocity of the bullet because:
Explanation: Since momentum of bullet must equal momentum of gun's recoil (m_bullet × v_bullet = m_gun × v_recoil), and the gun's mass is much larger, its recoil velocity is proportionally much smaller.
78. An inflated balloon released without tying its neck flies off rapidly in the opposite direction to the escaping air. This best illustrates:
Explanation: Air rushing out in one direction (action) generates a reactive thrust that propels the balloon in the opposite direction, just like rocket propulsion.
79. A man standing on a stationary boat jumps onto the shore, causing the boat to move backward into the water. This scenario best combines:
Explanation: The equal-and-opposite reaction force (Third Law) results in the boat and person gaining equal and opposite momenta, consistent with total momentum before the jump being zero (conserved).
80. Newton's Third Law of Motion primarily deals with the relationship between:
Explanation: The Third Law specifically describes the mutual, equal, and opposite forces exerted by two bodies interacting with each other.
SECTION V: Conservation of Momentum & Applications [Questions 81 to 100]
81. The Law of Conservation of Momentum states that in the absence of an external force, the total momentum of a system of interacting bodies:
Explanation: When no external force acts on a system, the total momentum before an event (like collision or explosion) equals total momentum after it.
82. For two bodies colliding in an isolated system, conservation of momentum implies:
Explanation: As long as no external force acts, the sum of momenta of the colliding bodies remains the same before and after the collision.
83. The Law of Conservation of Momentum can be derived directly from:
Explanation: The Second Law relates force to rate of change of momentum, and the Third Law's equal-opposite forces show that when combined for two interacting bodies, the total momentum change of the system is zero.
84. Before a gun is fired, the total momentum of the gun-bullet system is:
Explanation: Before firing, both the gun and bullet are at rest, so their combined initial momentum is zero.
85. When two moving objects collide and no external force acts on them, the total momentum of the system:
Explanation: In an isolated system with no external force, momentum is always conserved during any type of collision.
86. Rocket propulsion, where the rocket accelerates forward as gases are expelled backward, is best explained by:
Explanation: The backward momentum gained by ejected gases is balanced by an equal forward momentum gained by the rocket, keeping total momentum constant.
87. A bomb at rest explodes into two unequal fragments. According to conservation of momentum, the fragments will fly off:
Explanation: Since initial momentum was zero, the vector sum of the fragments' momenta after explosion must also be zero, meaning they move in opposite directions with momenta of equal magnitude.
88. The Law of Conservation of Momentum is strictly valid only when:
Explanation: Momentum conservation applies only to isolated systems where the net external force on the system is zero.
89. In a perfectly elastic collision, which quantities are conserved?
Explanation: A perfectly elastic collision conserves both the total momentum and total kinetic energy of the system.
90. In an inelastic collision (e.g., where two bodies stick together after impact):
Explanation: In inelastic collisions, momentum is always conserved, but some kinetic energy is converted into heat, sound, or deformation, so it is not conserved.
91. Two balls moving towards each other collide and stick together, moving as a single mass afterward. This type of collision is called:
Explanation: When colliding bodies stick together and move with a common velocity, it is termed a perfectly inelastic collision.
92. For two bodies of masses m₁ and m₂ moving with initial velocities u₁ and u₂ that collide and move with final velocities v₁ and v₂, the conservation of momentum equation is:
Explanation: The standard conservation of momentum equation equates the sum of initial momenta to the sum of final momenta of the two bodies.
93. The recoil velocity of a gun can be calculated using conservation of momentum, expressed as:
Explanation: Since initial total momentum is zero, m_gun × v_gun + m_bullet × v_bullet = 0, giving v_gun = −(m_bullet × v_bullet)/m_gun, the negative sign indicating opposite direction (recoil).
94. A bullet of mass 10 g is fired from a gun of mass 5 kg with a velocity of 400 m/s. What is the recoil velocity of the gun?
Explanation: Mass of bullet = 0.01 kg. By conservation of momentum: 5 × v = 0.01 × 400, so v = 4/5 = 0.8 m/s (opposite in direction to bullet).
95. A gun of mass M fires a bullet of mass m with velocity v. The recoil velocity of the gun (magnitude) is given by:
Explanation: From Mv_gun = mv_bullet (magnitudes, since initial momentum was zero), v_gun = mv/M.
96. A gun recoils backward when fired mainly because:
Explanation: As the bullet gains forward momentum, the gun must gain equal backward momentum to keep the total system momentum at its initial value of zero, in line with Newton's Third Law.
97. If the net external force acting on a system of bodies is zero, the total momentum of the system will:
Explanation: This is the direct statement of the Law of Conservation of Momentum — total momentum stays constant when no external force acts.
98. The principle of conservation of momentum is fundamentally used in the design and working of:
Explanation: Rockets and jet engines are propelled forward as a direct application of conservation of momentum, by expelling mass (fuel/exhaust) backward at high speed.
99. For an isolated system with no external force acting on it, the sum of momenta of all bodies in the system:
Explanation: This is the essence of the conservation law: in an isolated system, total momentum is a constant of motion, unaffected by internal interactions like collisions or explosions.
100. Seatbelts, airbags, and cushioned dashboards in vehicles are all designed using the same underlying physics principle of:
Explanation: All these safety devices work by extending the duration over which the passenger's momentum changes to zero during a collision, thereby lowering the average force experienced (F = Δp/Δt).

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