## Kinetic Energy

### Key Concepts

- What is kinetic energy?
- Examples of kinetic energy

**What is energy?**

Definition: In physics, energy is regarded as the capacity to do work. In general, energy is the utility of the body to do some work like moving, heating, etc.

Energy is represented by E, and the unit of energy is Joules in the SI system.

### Introduction to Energy

**We need energy:**

We all need the energy to do our daily works without interruption. Everything on the Earth possesses energy. Hence all the objects on the earth have some energy or want some energy to do work.

Energy is not only on the Earth but in space also. Every object has energy.

**When can we say that a body has the energy?**

We can say that a body has energy when there is a useful work outcome.

Energy is regarded as the capacity to do work.

### Explanation

**Kinetic energy:**

Let us consider a car which is moving on the road

Car A has the mass m and is moving from one place to another place.

- What is needed for a car to move from one place to another?

- What is the energy possessed by the car?

**Kinetic energy:**

To move a car A of mass **m** from one place to another with velocity **v**, the body should have the energy known as kinetic energy.

Kinetic energy is required for a body of mass to move with the velocity **v**, and kinetic energy changes with change in the motion of the body.

**Definition:**

Energy possessed by a body by virtue of its motion is called kinetic energy.

Where KE = kinetic energy

m= Mass

v= Velocity

Unit of the kinetic energy is joules.

**Important points of kinetic energy:**

- Kinetic energy is a virtue of a body’s motion.
- Kinetic energy can be zero or positive; it cannot be negative.
- Kinetic energy increases as the velocity increases, and the velocity is squared.

- If a body has kinetic energy, it should have velocity; without velocity, kinetic energy is zero.

**Examples of kinetic energy:**

**Example 1:**

Let us consider a footballer playing a football match, he kicks the ball towards the goalkeeper and he expects a goal.

- What is the energy possessed by football?

- If the football has a mass of 2 kg and the footballer has hit the ball with a velocity of 6 m/s, then find the kinetic energy of the body.

The energy possessed by the football is the kinetic energy as the kinetic energy is the energy possessed by the body by virtue of its position.

Given that the mass of the football is 2 kg and the velocity at which the balls was hit was 6 m/s, then the kinetic energy is given by:

**Example 2:**

let us consider a train in the railway station which is moving from the platform with the velocity of 4 m/s and attains the velocity of 10 m/s, if the train has a mass of 3000 kg, then find the kinetic energy of the body?

Given the train has an initial velocity of 4 m/s and the mass of the train is 3000 kg, then the kinetic energy is

and also, the train attains the velocity of 10 m/s, then the kinetic energy is

The total kinetic energy is :

## Summary:

**Definition:**Energy possessed by a body by virtue of its motion is called kinetic energy.

Where KE= kinetic energy

m = Mass

v=Velocity

Unit of the kinetic energy is joules.

**Important points of kinetic energy:**

- Kinetic energy is the virtue of a body’s motion.
- Kinetic energy can be zero or positive; it cannot be negative.
- Kinetic energy increases as the velocity increases, and the velocity is squared.
- If a body has kinetic energy, it should have velocity; without velocity, kinetic energy is zero.

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