Previous Year NEET Questions on Laws of Motion

Explanation: When a ball is dropped onto the ground, it undergoes a collision that involves forces acting between the ball and the surface. According to Newton’s third law of motion, every action has an equal and opposite reaction. As the ball hits the ground, it exerts a force downward on the surface. In response, the ground exerts an upward force on the ball. This interaction is responsible for the change in motion.

During impact, the ball compresses slightly, storing energy in the form of elastic potential energy. This stored energy is then released as the ball regains its original shape, pushing it upward. The efficiency of this energy conversion determines how high the ball rebounds. Materials like rubber are more elastic, so they bounce higher compared to less elastic materials.

For example, when you press a rubber ball against a hard surface and release it, it quickly regains its shape and moves upward. Similarly, when dropped, the deformation and restoration process causes the bounce.

In summary, the bouncing of a ball is due to the interaction of forces during impact and the conversion of energy between kinetic and elastic forms.

Explanation: Momentum is a fundamental concept in Physics that describes the quantity of motion an object possesses. It depends on both Mass and velocity. When two objects move with the same speed, their momentum is influenced only by their masses, since velocity remains constant for both.

The relationship between momentum, Mass, and velocity is given by the formula p = mv, where p represents momentum, m is Mass, and v is velocity. Since velocity is identical for both objects, any difference in momentum must arise from differences in Mass. A larger Mass results in greater momentum.

Consider two carts moving at the same speed, where one cart is loaded with extra weight. The heavier cart is harder to stop or change direction compared to the lighter one, indicating it has greater momentum. This demonstrates how Mass directly affects momentum when speed is constant.

Thus, when comparing two objects moving at equal speeds, the one with greater Mass will possess proportionally greater momentum, as determined by the relationship between Mass and motion.

Explanation: The sensation of feeling heavier or lighter in an elevator is related to the concept of apparent weight, which depends on the forces acting on the body. Normally, a person’s weight is due to gravity, but in a moving elevator, additional forces come into play due to acceleration.

When the elevator accelerates upward, the floor pushes against the person with greater force than usual. This increased normal reaction force makes the person feel heavier. Conversely, when the elevator accelerates downward, the normal force decreases, making the person feel lighter. If the elevator moves at constant speed, there is no acceleration, and the apparent weight remains equal to the actual weight.

For instance, when an elevator just begins to move upward, there is a brief moment where the upward acceleration increases the force felt by the person. This creates the sensation of being heavier than usual.

In summary, the feeling of increased weight occurs when the elevator accelerates upward, as the supporting force acting on the body becomes greater than the normal gravitational force.

Explanation: When an object is suspended by a rope, the forces acting on it must balance for the system to remain in equilibrium. The weight of the object acts downward due to gravity, while the tension in the rope provides support. In this case, the rope is held horizontally, which creates a unique situation.

For a rope to remain perfectly horizontal, the vertical components of the tension must balance the entire weight of the object. However, if the rope is completely straight, the angle between the rope and horizontal becomes zero. This means there is no vertical component of tension to support the weight.

As a result, the tension required must increase significantly to provide the necessary upward force. Mathematically, as the angle approaches zero, the tension required approaches extremely large values. This is because only a tiny vertical component is available to counteract the weight.

A useful analogy is trying to hold a heavy object using a nearly horizontal string—the flatter the string, the harder it becomes to support the weight.

In summary, maintaining a perfectly horizontal rope while supporting weight requires extremely large tension due to the absence of sufficient vertical force components.

Explanation: The relationship between force and acceleration is a fundamental principle described by Newton’s second law of motion. It states that the acceleration of an object depends on the NET force acting on it and its mass. When a force is applied, it changes the velocity of the object, resulting in acceleration.

Mathematically, this relationship is expressed as F = ma, where F is force, m is mass, and a is acceleration. From this equation, it can be understood that acceleration increases when the applied force increases, provided the mass remains constant.

For example, if you push a shopping cart with greater force, it accelerates more quickly. If the same force is applied to a heavier cart, the acceleration is less, showing that mass resists changes in motion.

Thus, acceleration is directly linked to the magnitude of the applied force. A larger force produces a greater acceleration in the same direction as the force.

In summary, the acceleration of an object increases proportionally with the applied NET force, as described by Newton’s second law of motion.

Explanation: The resultant force on an object refers to the overall effect of all forces acting on it. Instead of considering each force separately, they are combined to produce a single equivalent force that has the same effect on motion. This is also known as the NET force.

When multiple forces act on an object, they can either reinforce or oppose each other. If forces act in the same direction, they add up. If they act in opposite directions, they subtract from each other. The final combined effect determines how the object moves.

For instance, if two people push a box in the same direction, the total force increases. If one pushes while another pulls in the opposite direction, the NET effect depends on the difference between the forces.

The resultant force is responsible for causing acceleration according to Newton’s second law. If the resultant force is zero, the object remains at rest or continues moving with constant velocity.

In summary, the resultant force represents the combined effect of all forces acting on an object, determining its motion or state of rest.

Explanation: Newton’s laws of motion are highly effective in describing the motion of everyday objects at ordinary speeds. These laws are based on classical mechanics, which assumes that time and space are absolute and that speeds involved are much smaller than the speed of Light.

However, when objects move at extremely high velocities, close to the speed of Light, classical mechanics no longer provides accurate results. In such cases, relativistic effects become significant, and Einstein’s theory of relativity must be used to describe motion accurately.

At very high speeds, properties like mass, time, and length behave differently compared to everyday experiences. For example, time dilation and length contraction occur, which are not accounted for in Newtonian mechanics.

An analogy is using simple arithmetic for small calculations but needing advanced mathematics for complex problems. Similarly, Newton’s laws are replaced by relativistic Physics under extreme conditions.

In summary, Newton’s laws are limited to low-speed scenarios and fail to accurately describe motion at speeds approaching that of Light.

Explanation: When a car takes a sharp turn, passengers experience a sideways motion due to inertia, which is the tendency of an object to resist changes in its state of motion. According to Newton’s first law, an object in motion continues in a straight line unless acted upon by an external force.

As the car changes direction, the passengers’ bodies tend to continue moving in their original straight-line path. This creates the sensation of being pushed sideways relative to the car. The car changes direction due to frictional force between the tires and the road, but the passengers’ bodies momentarily lag behind.

For example, when a bus turns suddenly, passengers often lean or slide to one side. This is not because a force pushes them outward, but because their bodies resist the change in direction.

Seat belts and friction between the seat and the body help counteract this effect by providing the necessary force to change direction.

In summary, the sideways motion during a turn is caused by inertia, as the body resists the change in direction of the moving vehicle.

Explanation: The law of conservation of momentum is a fundamental principle in Physics that applies to isolated systems where no external forces act. Momentum, defined as the product of mass and velocity, represents the motion of an object.

According to this law, the total momentum of a system remains constant if no external force influences it. This means that the combined momentum before any interaction, such as a collision, is equal to the combined momentum after the interaction.

During collisions, momentum may be transferred between objects, but the total value does not change. For example, when two billiard balls collide, one may slow down while the other speeds up, but the total momentum remains the same.

This principle is widely used to analyze collisions, explosions, and other interactions in Physics. It helps predict outcomes based on initial conditions.

In summary, the law states that in the absence of external forces, the total momentum of a system remains unchanged throughout any interaction.

Explanation: Jet engines and rockets are propulsion systems that generate motion by expelling gases at high speed, based on Newton’s third law of motion. However, their working mechanisms differ significantly, especially in how they obtain oxygen for combustion.

Jet engines operate by taking in air from the Atmosphere, compressing it, mixing it with fuel, and igniting the mixture. This means they depend on the presence of atmospheric oxygen to function effectively. Without air, such as in space, jet engines cannot operate.

Rockets, on the other hand, carry both fuel and an oxidizer, allowing them to burn fuel without relying on atmospheric oxygen. This enables rockets to function in space, where there is no air.

A simple analogy is that a jet engine is like a fire that needs surrounding air to burn, whereas a rocket is like a self-contained system carrying everything required for combustion.

In summary, both systems rely on gas expulsion for motion, but differ in their dependence on atmospheric oxygen for operation.