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The energy of a body due to its motion is called kinetic enerrgy

Every moving body posseses kinetic energy

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Example 1
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A ball kept at ground does not have kinetic enrgy

But a ball thrown at batsmen has kinetic energy

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Example 2
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A bullet kept in a gun does not have kietic energy

But a bullet fired from gun has kinetic energy

## How to measure kinetic energy of a moving body

It is the amount of work a body can do before coming to rest

Example

If we kick a football, it travels some distance before coming to a rest

Work done by football in travelling a distance before coming to rest is kinetic energy

In this case, when football is kicked,it has certain initial velocity u

When ball stops, its final velocity v becomes 0

## Formula for Calculating Kinetic Energy

The formula for Kinetic energy is

Kinetic Energy = 1/2 × Mass × Velocity^2

Kinetic Energy = 1/2 × mv^2

## How is this formula derived

To derive this formula, we use the relation between Kinetic Energy and Work Done

Kinetic Energy of a body moving with a certain velocity is equal to work done on it to acquire that velocity

Let's see its derivation

Note: While doing questions, we use

Change in Kinetic Energy = Work Done

##

Questions

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Q 1 Page 152 -
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What is the kinetic energy of an object?

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Q 2 Page 152 -
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Write an expression for the kinetic energy of an object

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Q 3 Page 152 -
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The kinetic energy of an object of mass, m moving with a velocityof 5 m s–1 is 25 J. What will be its kinetic energy when its velocityis doubled? What will be its kinetic energy when its velocity is increased three times?

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Example 11.3 -
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An object of mass 15 kg is moving with a uniform velocity of 4 m s–1. What is the kinetic energy possessed by the object?

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Example 11.4 -
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What is the work to be done to increase the velocity of a car from30 km h–1 to 60 km h–1 if the mass of the car is 1500 kg?

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NCERT Question 4 -
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Certain force acting on a 20 kg mass changes its velocity from 5 m s–1 to 2 m s–1. Calculate the work done by the force.

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NCERT Question 16 -
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An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?

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NCERT Question 17 -
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Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?