Law Of Motion — Part 1 MCQs with Explanations

Let's understand why Option A is the correct answer and what Newton's Third Law of Motion is all about. Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction . This means whenever one object pushes or pulls another object (the action), the second object pushes or pulls back on the first object with the same strength but in the opposite direction (the reaction). These forces always come in pairs and act on different objects. Let's look at the options: Option A: When a person jumps from the boat to the river, the boat goes backwards. This is a perfect example of Newton's Third Law . Action: The person pushes the boat backwards with their feet to jump forward. Reaction: The boat, in turn, pushes the person forward , allowing them to jump. At the same time, because of the force the person applied, the boat moves backwards. The forces are equal in strength and opposite in direction, acting on two different objects (person on boat, boat on person). Option B: Passengers standing in a bus fall in the back direction, when the stationary bus suddenly moves. This situation is explained by Newton's First Law of Motion , also known as the Law of Inertia. When the bus suddenly moves forward, the passengers' bodies tend to stay in their original state of rest due to inertia, making them fall backward relative to the bus. Option C: When a person falls on the cement floor, he gets hurt. This relates to Newton's Second Law of Motion and the concept of impact. When a person falls on a hard surface like cement, the stopping time (the time it takes for their body to stop moving) is very short. A very short stopping time leads to a very large force being exerted on the person, causing injury. If the stopping time were longer (like falling on a soft mat), the force would be smaller. Option D: While catching a fast moving cricket ball, a fielder puts his hands backwards. This is also explained by Newton's Second Law of Motion . By moving his hands backward, the fielder increases the time it takes for the ball to stop. When the time of impact is increased, the average force exerted by the ball on the fielder's hands is reduced, which helps prevent injury. Therefore, only Option A directly demonstrates the "action-reaction pair" principle of Newton's Third Law .

The correct answer is A: Isaac Newton . This question refers to one of the most fundamental laws in physics: Newton's Third Law of Motion . Newton's Third Law states: For every action, there is an equal and opposite reaction. This means that if object A exerts a force on object B, then object B simultaneously exerts a force equal in magnitude and opposite in direction on object A. Isaac Newton formulated this law, along with his other laws of motion, which are the foundation of classical mechanics. Let's look at why the other options are incorrect: Albert Einstein is famous for his theory of relativity, particularly E=mc², not Newton's Laws of Motion. Niels Bohr is known for his model of the atom and contributions to quantum mechanics. Duncan Haldane is a more recent Nobel laureate known for his work in condensed matter physics, specifically topological phases of matter. Therefore, the answer is definitively Isaac Newton .

1. When a car turns on a curved road, the passengers feel a force that appears to push them outward, away from the center of the curve. This force is commonly referred to as centrifugal force. 2. Centrifugal force is not a real force but is rather a perceived force experienced due to the inertia of the passengers. It is the result of the tendency of an object to move in a straight line while the car is changing direction. 3. The sensation of this force is due to the inertia of the passengers' bodies, which want to continue moving in a straight line. As the car turns, the passengers feel pushed to the outside of the curve. 4. The other options are not correct because: - Inertia is the property of an object to resist changes in its state of motion, but it is not the force that passengers feel. - Centripetal force is the force that acts towards the center of the curve, keeping the car (and passengers) on the curved path. It is not the force felt by passengers; rather, it is the force responsible for making the turn possible. - Gravitational force is the force of attraction between objects due to their masses and does not relate to the sensation experienced when turning on a curved road. Thus, the correct answer is Option A: centrifugal force.

1. To find the distance traveled by the ant in one day, we need to convert its speed from cm/sec to m/day. 2. The given speed of the ant is 75 cm/sec. To find the distance traveled in one day, we need to calculate how many seconds are in a day. 3. There are 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute, so: 24 × 60 × 60 = 86400 seconds in a day. 4. Now, we can calculate the distance traveled in a day by multiplying the speed by the total number of seconds in a day: 75 cm/sec × 86400 sec/day = 6480000 cm/day. 5. To convert the distance from cm to m, we divide by 100 (since 1 m = 100 cm): 6480000 cm/day ÷ 100 = 64800 m/day. 6. Therefore, the correct answer is Option A: 64800 m/day.

Understanding Newton's Third Law: Newton's Third Law of Motion states that for every action, there's an equal and opposite reaction. Let's break down the question: A 70 kg man (let's call him Man A) pushes a 50 kg man (Man B) with a force of 50N. This 50N force is the 'action'. According to Newton's Third Law, Man B will push back on Man A with an equal and opposite force. This means Man B also pushes Man A with a force of 50N . Therefore, the answer is A: 50N The masses of the men are irrelevant to the force of the reaction; only the action force matters when applying Newton's Third Law.

When a mass is attached to the midpoint of a rope held horizontally by two persons, it causes the rope to deviate from the horizontal direction due to the force of gravity acting on the mass. To completely straighten the rope, the tension in the rope must counteract the gravitational force acting on the mass. Since the mass is 20 kg and the acceleration due to gravity (g) is 10 m/s 2 , the gravitational force on the mass is given by F=mg, where m=20kg and g=10m/s 2 . Therefore, F=20×10=200N So, the tension required to completely straighten the rope is 200 N .

The correct answer is Option B: Newton's first law of motion . Let's understand why: What is Force? Imagine pushing a toy car or pulling a door. That push or pull is what we call a force . A force can make things move, stop, or change direction. Newton's First Law of Motion , also known as the Law of Inertia , is very important for understanding force. It states: An object that is not moving (at rest) will stay not moving, and an object that is moving will keep moving at the same speed and in the same direction, unless an unbalanced force acts on it . Think about it: * If a ball is sitting on the ground, it won't move unless someone kicks it (applies a force). * If a spacecraft is moving in empty space, it will keep moving forever at the same speed and direction unless something (like another force from a planet's gravity) makes it change. So, this law clearly tells us what a force *does*: it is the cause that makes an object change its state of motion (either starting to move, stopping, speeding up, slowing down, or changing direction). Because it explains what *causes* a change in motion, it helps us define force as that cause. Let's quickly see why other options are not the best answer for the *definition* of force: * Newton's Second Law of Motion (F=ma): This law helps us measure force and tells us *how much* an object will accelerate when a force acts on it. It describes the *effect* of force, not its basic definition. * Newton's Third Law of Motion: This law tells us that for every action, there is an equal and opposite reaction. It describes how forces interact between two objects , but not what force itself is in the first place. * Newton's Law of Gravity: This describes a specific type of force (gravity) and how it works, not the general definition of what *any* force is.

Understanding Average Speed: Average speed isn't just the simple average of two speeds. It's about the total distance covered divided by the total time taken. Let's break it down: Imagine the distance between A and B is 120 km (we can choose any distance, this makes the calculation easy). Going from A to B: Speed = 40 km/h Distance = 120 km Time = Distance / Speed = 120 km / 40 km/h = 3 hours Returning from B to A: Speed = 60 km/h Distance = 120 km Time = Distance / Speed = 120 km / 60 km/h = 2 hours Calculating Average Speed: Total distance = 120 km + 120 km = 240 km Total time = 3 hours + 2 hours = 5 hours Average speed = Total distance / Total time = 240 km / 5 hours = 48 km/h Therefore, the correct answer is B: 48 km/h Remember: Average speed depends on both the distance and the time taken for each part of the journey. It's not simply adding the speeds and dividing by two.

* Option A: Momentum - Momentum depends on both mass and velocity . Even though the spheres fall at the same rate, the iron sphere has a greater mass, so its momentum will be higher. * Option B: Acceleration - Acceleration due to gravity (g) is constant for all objects near the Earth's surface, regardless of their mass (assuming air resistance is negligible). Both spheres are acted upon by the same gravitational force per unit mass, meaning they will accelerate downwards at the same rate (approximately 9.8 m/s²). * Option C: Kinetic Energy - Kinetic energy depends on both mass and velocity squared (KE = 1/2 * m * v²). Since the iron sphere has a greater mass, it will have a greater kinetic energy even if they have the same velocity. * Option D: Potential Energy - Potential energy depends on mass , gravity , and height (PE = m * g * h). At the same height, the iron sphere has a greater mass, so it will have more potential energy. Therefore, the correct answer is B: acceleration. Because both spheres are falling under the influence of gravity alone (ignoring air resistance), they experience the same acceleration.

The correct answer is Option B: angular velocity . Moment of Inertia (I): Think of it as how resistant an object is to changes in its rotation. A higher moment of inertia means it's harder to start or stop the object from spinning. Factors Affecting Moment of Inertia: * Axis of Rotation: The moment of inertia changes depending on *where* you're trying to rotate the object around. It's easier to spin a door around its hinges than around an axis through the middle of the door. So, it depends on the axis of rotation. * Form of Mass: This essentially means the shape of the object. A solid sphere will have a different moment of inertia than a hollow sphere of the same mass and radius. Thus, it depends on form of mass * Distribution of Mass: This is super important! How the mass is spread out affects the moment of inertia. If more of the mass is concentrated further from the axis of rotation, the moment of inertia is higher. So, it depends on mass distribution * Angular Velocity: This is how *fast* the object is already spinning. The moment of inertia is a property of the object *itself*. It doesn't change based on how fast the object is spinning. In simple terms: Imagine you're holding a dumbbell. How hard it is to *start* spinning that dumbbell (moment of inertia) depends on how it's shaped and where the weight is (mass distribution, form of mass and axis of rotation), but *not* on how fast it's already spinning (angular velocity).

Imagine you're standing on a perfectly smooth, icy surface – that's what a frictionless surface is like. Friction is what helps your feet grip the ground when you walk or run. Without friction, your feet would just slide. Let's analyze each option: Option A: Sneezing Sneezing involves internal forces within your body. These forces won't move you on a frictionless surface because there's no external force to push against. This option is incorrect. Option B: Jumping When you jump, you push down on the ground (action). The ground pushes back up on you (reaction), and this reaction force propels you upward even without friction. This is due to Newton's Third Law of Motion. On a frictionless surface, jumping causes you to move upward, but due to the lack of friction, you also move horizontally a little bit. This option is correct. Option C: Running Running relies on friction between your feet and the ground to propel you forward. Without friction, your feet would just slip. This option is incorrect. Option D: Rolling Similar to running, rolling needs friction to work. You wouldn't roll effectively on a frictionless surface. This option is incorrect. Conclusion: The only way to move on a frictionless surface is by using an action that creates an equal and opposite reaction, as described in Newton's Third Law. Jumping is the only option that does this. Therefore, the correct answer is Option B: Jumping.

The correct answer is (C) class-III lever . First, what is a lever? A lever is a simple machine that amplifies an applied force. There are three classes of levers, distinguished by the relative positions of the fulcrum (pivot point) , the load (resistance) , and the effort (force applied) . * Class-I Lever: The fulcrum is between the load and the effort. Think of a seesaw. * Class-II Lever: The load is between the fulcrum and the effort. Think of a wheelbarrow. * Class-III Lever: The effort is between the fulcrum and the load. Think of your arm when lifting something or tongs . Now, think about a ladder being used. The fulcrum is the bottom of the ladder resting on the ground. The load is at the top of the ladder where someone is working (or where it rests against a wall). The effort is where you are applying the force to climb the ladder, which is between the bottom (fulcrum) and the top (load). Since the effort is between the fulcrum and the load, a ladder acts as a class-III lever . An inclined plane (Option D) is also a simple machine, but a ladder's primary function involves lever action when climbing.

In the absence of gravitational force of attraction, propulsion on the rocket is stable. This is because: according to Newton's third law of motion, every action has an equal and opposite reaction. As the rocket expels exhaust gases: in one direction, an equal and opposite force propels the rocket in the opposite direction. Therefore, the propulsion of a rocket is stable even in the absence of gravitational attraction.

The question is asking about the acceleration of a particle moving in a circle at a constant speed . Important Point: Even though the speed is constant, the velocity isn't! Velocity includes both speed AND direction. Since the particle is moving in a circle, its direction is constantly changing. Because the direction is changing, the particle is accelerating. This acceleration is called centripetal acceleration , and it always points towards the center of the circle. Now, the formula for centripetal acceleration is: a = v 2 / r Where: * a is the centripetal acceleration * v is the speed of the particle * r is the radius of the circle So, let's look at the options: Option A: zero - Incorrect because we know there *is* acceleration. Option B: v/r - Incorrect . This is not the correct formula. Option C: v/r 2 - Incorrect . This is not the correct formula. Option D: v 2 /r - Correct! This matches the formula for centripetal acceleration. Therefore, the answer is D. The acceleration of the particle is v 2 /r.

The question asks about the percentage increase in displacement of a particle moving with uniform acceleration . It compares the distance covered in the 6th second to the distance covered in the 5th second . Understanding the Concept: Since the particle starts from rest and has uniform acceleration , it means its velocity increases at a constant rate. The distance covered in each successive second will keep increasing. Formula to Use: The distance traveled in the *n*th second (Sn) can be calculated using the formula: Sn = u + (a/2)(2n - 1) Where: * u = initial velocity (0 in this case, since it starts from rest) * a = acceleration * n = the second you are interested in Calculations: Distance in 5th second (S5) = 0 + (a/2)(2*5 - 1) = (a/2) * 9 = 4.5a Distance in 6th second (S6) = 0 + (a/2)(2*6 - 1) = (a/2) * 11 = 5.5a Percentage Increase: Percentage increase = [(S6 - S5) / S5] * 100 Percentage increase = [(5.5a - 4.5a) / 4.5a] * 100 Percentage increase = (a / 4.5a) * 100 Percentage increase = (1 / 4.5) * 100 Percentage increase ≈ 22.22% Answer: Therefore, the percentage increase is approximately 22% . So the correct answer is Option B: 22%

First, what does "constant velocity" mean? It means the object is moving at a steady speed AND in a steady direction. Let's look at each option: Option A: Its motion is along a straight line If the velocity is constant (steady speed and direction), the object *must* be moving in a straight line. If it curved, the direction would be changing, and thus the velocity wouldn't be constant. So, this statement IS correct. Option B: Its speed changes with time If the velocity is *constant*, the speed *cannot* change. The speed is staying the same. So, this statement is NOT correct, and likely our answer. Option C: Its acceleration is zero Acceleration is the rate of change of velocity. If the velocity isn't changing (it's constant), then the acceleration is zero. So, this statement IS correct. Option D: Its displacement increases linearly with time Displacement is the change in position. If you're moving at a steady speed in a straight line, the distance you cover (displacement) increases at a steady rate. That's what "linearly" means. So, this statement IS correct. Therefore, the answer is Option B: Its speed changes with time . Because with constant velocity, the speed cannot change.

The statement "The force between two objects is always equal and opposite" refers to Newton's third law of motion . This law states that for every action, there is an equal and opposite reaction. In other words, when one object exerts a force on another object, the second object exerts a force of equal magnitude but in the opposite direction on the first object. Option B: Second law of motion Newton's second law of motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This law does not specifically address the concept of equal and opposite forces between two objects. Option C: First and second law of motion While both the first and second laws of motion are fundamental principles in classical mechanics, neither of them directly addresses the idea of forces being equal and opposite between two objects. Option D: First law of motion Newton's first law of motion, also known as the law of inertia, states that an object at rest will remain at rest, and an object in motion will remain in motion with the same velocity unless acted upon by an external force. This law does not directly address the concept of equal and opposite forces between two objects. Therefore, the correct answer is Option A: Third law of motion .

It is helpful to understand the effects of force is the correct answer to “Newton's second law of motion:”. This question is standard in competitive examination syllabi for Law Of Motion.

uniform speed, variable velocity is the correct answer to “The motion of a body around a circular path is an example of”. This question is standard in competitive examination syllabi for Law Of Motion.

Applied force is the correct answer to “The rate of change in momentum of a body is proportional to . . . . . . . .”. This question is standard in competitive examination syllabi for Law Of Motion.

the force exerted by a charged body is the correct answer to “Electrostatic force is”. This question is standard in competitive examination syllabi for Law Of Motion.

The velocity of the object is constant is the correct answer to “Zero acceleration means . . . . . . . .”. This question is standard in competitive examination syllabi for Law Of Motion.

- 1 m/s2 is the correct answer to “Consider the following velocity and time graph. Which one of the following is the value of average acceleration from 8 s' to 12 s”. This question is standard in competitive examination syllabi for Law Of Motion.

inertia is the correct answer to “The stock of books lying on the table does not move due to . . . . . . . .”. This question is standard in competitive examination syllabi for Law Of Motion.

7 ms-2 is the correct answer to “What will be the acceleration produced when a force of 21 N is applied on an object of mass 3 kg”. This question is standard in competitive examination syllabi for Law Of Motion.

Newton's first law of motion is the correct answer to “When a stationary bus starts moving, the people standing in it fall in the back direction. Which of the following law explains this situation”. This question is standard in competitive examination syllabi for Law Of Motion.

1687 is the correct answer to “What was the year of publication of Newton's laws of motion”. This question is standard in competitive examination syllabi for Law Of Motion.

If the car is moving an straight road is the correct answer to “In which of the following cases of motions, the distance and displacement are equal”. This question is standard in competitive examination syllabi for Law Of Motion.

A cricket ball is the correct answer to “Which one of the following has maximum inertia”. This question is standard in competitive examination syllabi for Law Of Motion.

CD and AB is the correct answer to “In the given Velocity (v) versus Time (t ) graph, accelerated and decelerated motions are respectively represented by line segments.”. This question is standard in competitive examination syllabi for Law Of Motion.

45° with horizontal is the correct answer to “The angle in which a cricket ball should be hit to travel maximum horizontal distance is”. This question is standard in competitive examination syllabi for Law Of Motion.

Rocket launching is the correct answer to “Which of the following is an example of Newton's third law of motion:”. This question is standard in competitive examination syllabi for Law Of Motion.

Newton's Third law is the correct answer to “The movement of a horse lawn carriage is an example of which principle of physics.”. This question is standard in competitive examination syllabi for Law Of Motion.

the resultant would be zero is the correct answer to “If action and reaction were to act on the same body . . . . . . . .”. This question is standard in competitive examination syllabi for Law Of Motion.

Newton's First Law of Motion is the correct answer to “If no net force acts on a body, then the velocity of the body cannot change. This law is known as”. This question is standard in competitive examination syllabi for Law Of Motion.

Horizontal component of velocity is the correct answer to “A ball is thrown upwards and it returns to ground describing a parabolic path. Which of the following remains constant”. This question is standard in competitive examination syllabi for Law Of Motion.

Instantaneous acceleration is the correct answer to “The acceleration of a particle at a particular instant of time is called”. This question is standard in competitive examination syllabi for Law Of Motion.

Only 1 is the correct answer to “Consider the following statements. 1. For a moving particle, distance can never be negative or zero while displacement can be. 2. The rate of displacement with time is called speed. 3. For a moving body the average velocity can never be negative or zero. Which of the statements given above is/are correct”. This question is standard in competitive examination syllabi for Law Of Motion.

uneven speed is the correct answer to “If an object covers an uneven distance in the same time interval, it is called . . . . . . . .”. This question is standard in competitive examination syllabi for Law Of Motion.

Newton's Second Law of Motion is the correct answer to “The rate of change of momentum of an object is proportional to the applied unbalanced force in the direction of the force. This rule is known as:”. This question is standard in competitive examination syllabi for Law Of Motion.