# 9 Lecture

## Collisions

Collisions are an essential concept in physics, particularly in mechanics. A collision is defined as an event where two or more bodies come into contact and exchange energy or momentum.

## Important Mcq's Midterm & Finalterm Prepration Past papers included

Which of the following is a type of collision?

a) Elastic collision

b) Inelastic collision

c) Both A and B

d) None of the above

Answer: c) Both A and B

In an elastic collision, which of the following is conserved?

a) Momentum

b) Kinetic energy

c) Both A and B

d) None of the above

Answer: c) Both A and B

In an inelastic collision, which of the following is conserved?

a) Momentum

b) Kinetic energy

c) Both A and B

d) None of the above

Which of the following statements is true regarding an elastic collision?

a) The objects stick together after the collision.

b) The kinetic energy is conserved.

c) The momentum is conserved.

d) None of the above

Answer: c) The momentum is conserved.

Which of the following statements is true regarding an inelastic collision?

a) The objects stick together after the collision.

b) The kinetic energy is conserved.

c) The momentum is conserved.

d) None of the above

Answer: a) The objects stick together after the collision.

Which of the following is an example of an inelastic collision?

a) A ball bouncing off a wall

b) A car hitting a wall and crumpling

c) A satellite orbiting the Earth

d) None of the above

Answer: b) A car hitting a wall and crumpling

Which of the following is an example of an elastic collision?

a) A ball bouncing off a wall

b) A car hitting a wall and crumpling

c) A satellite orbiting the Earth

d) None of the above

Answer: a) A ball bouncing off a wall

Which of the following is an example of a completely inelastic collision?

a) A ball bouncing off a wall

b) A car hitting a wall and crumpling

c) A satellite orbiting the Earth

d) None of the above

Answer: b) A car hitting a wall and crumpling

Which of the following is an example of a perfectly elastic collision?

a) A ball bouncing off a wall

b) A car hitting a wall and crumpling

c) A satellite orbiting the Earth

d) None of the above

Answer: a) A ball bouncing off a wall

Which of the following statements is true regarding the conservation of momentum in a collision?

a) The total momentum of the system is always conserved.

b) The momentum of each object in the system is conserved.

c) Both A and B

d) None of the above

Answer: a) The total momentum of the system is always conserved.

## Subjective Short Notes Midterm & Finalterm Prepration Past papers included

What is meant by an elastic collision?

Answer: An elastic collision is one in which both kinetic energy and momentum are conserved.

What is the difference between an elastic and inelastic collision?

Answer: In an elastic collision, both momentum and kinetic energy are conserved, whereas in an inelastic collision, only momentum is conserved.

What is the law of conservation of momentum?

Answer: The law of conservation of momentum states that the total momentum of a system of objects is conserved if there are no external forces acting on the system.

What happens to the total momentum of a system of objects during a collision?

Answer: The total momentum of a system of objects is conserved during a collision.

What is the difference between a head-on collision and a rear-end collision?

Answer: In a head-on collision, two objects collide with each other while moving in opposite directions, whereas, in a rear-end collision, one object collides with another object from behind.

Can kinetic energy be conserved during an inelastic collision?

Answer: No, kinetic energy is not conserved during an inelastic collision.

What is the difference between a perfectly inelastic collision and a partially inelastic collision?

Answer: In a perfectly inelastic collision, the objects stick together after the collision, whereas in a partially inelastic collision, the objects do not stick together but some kinetic energy is lost.

What is the difference between a one-dimensional collision and a two-dimensional collision?

Answer: In a one-dimensional collision, the objects collide along a straight line, whereas in a two-dimensional collision, the objects collide in a plane.

What is the difference between a center of mass and a reference frame?

Answer: A center of mass is the point at which the mass of an object is concentrated, whereas a reference frame is a coordinate system used to describe the motion of an object.

Can momentum be conserved in a system with external forces acting on it?

Answer: No, momentum cannot be conserved in a system with external forces acting on it, as the external forces will cause a change in momentum.

Collisions are an essential concept in physics, particularly in mechanics. A collision is defined as an event where two or more bodies come into contact and exchange energy or momentum. The study of collisions in physics is important in various fields, including engineering, astronomy, and particle physics. In this article, we will discuss the types of collisions and their characteristics.

### Elastic Collisions

In an elastic collision, the total kinetic energy of the colliding bodies is conserved. The colliding bodies experience a force for a short duration of time, which changes the direction and speed of the bodies. However, the total kinetic energy of the system remains constant. The following equation represents the conservation of kinetic energy for an elastic collision: KEi = KEf where KEi represents the initial kinetic energy of the system, and KEf represents the final kinetic energy of the system.

### Inelastic Collisions

In an inelastic collision, the kinetic energy of the colliding bodies is not conserved. During the collision, some of the kinetic energy is converted to other forms of energy, such as heat or sound. The total kinetic energy of the system decreases after the collision. The following equation represents the conservation of momentum for an inelastic collision: pi = pf where pi represents the initial momentum of the system, and pf represents the final momentum of the system.

### Characteristics of Collisions

The following are the characteristics of collisions: Momentum Conservation The principle of momentum conservation states that the total momentum of a system of bodies is conserved if no external forces act on the system. The momentum of the system before the collision is equal to the momentum of the system after the collision. This principle applies to both elastic and inelastic collisions. Kinetic Energy Conservation In an elastic collision, the total kinetic energy of the system is conserved. However, in an inelastic collision, the total kinetic energy of the system decreases due to the conversion of kinetic energy into other forms of energy. Coefficient of Restitution The coefficient of restitution is a dimensionless quantity that represents the ratio of the relative velocity of separation to the relative velocity of approach of two colliding bodies. It is denoted by the symbol 'e' and is used to determine the type of collision. Elasticity The elasticity of a body is its ability to return to its original shape and size after deformation. In an elastic collision, the colliding bodies regain their original shape and size after the collision. Inelasticity In an inelastic collision, the colliding bodies do not regain their original shape and size after the collision. Perfectly Inelastic Collision A perfectly inelastic collision is a type of inelastic collision where the colliding bodies stick together after the collision. Center of Mass The center of mass of a system is the point where the entire mass of the system is considered to be concentrated. During a collision, the center of mass of the system remains unchanged. Impulse Impulse is defined as the product of force and time. During a collision, the colliding bodies experience a force for a short duration of time, which changes the direction and speed of the bodies. Law of Conservation of Energy The law of conservation of energy states that energy can neither be created nor destroyed. During a collision, the total energy of the system remains constant, but the energy may be converted from one form to another. Law of Conservation of Momentum The law of conservation of momentum states that the total momentum of a system of bodies is conserved if no external forces act on the system. During a collision, the momentum of the system is conserved.