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The energy of a body due to its motion is called kinetic enerrgy
Every moving body posseses kinetic energy
Example 1
A ball kept at ground does not have kinetic enrgy
But a ball thrown at batsmen has kinetic energy
Example 2
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
Q 1 Page 152 - What is the kinetic energy of an object?
Q 2 Page 152 - Write an expression for the kinetic energy of an object
Q 3 Page 152 - The kinetic energy of an object of mass, m moving with a velocity of 5 m s–1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?
Example 11.3 - 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?
Example 11.4 - What is the work to be done to increase the velocity of a car from 30 km h–1 to 60 km h–1 if the mass of the car is 1500 kg?
NCERT Question 4 - 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.
NCERT Question 16 - 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?
NCERT Question 17 - Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 km/h?
