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## What is Acceleration

It is the rate of change in velocity over time

Formula for Acceleration

Acceleration = Change in Velocity/Time Taken

Acceleration = (Final Velocity - Initial Velocity)/Time Taken

a = (v - u)/t

where

v = Final Velocity

u = Initial Velocity

t = time taken

What is Unit of Measurement of Acceleration

it is m/s
^{
2
}

(We know that formula for velocity is m/s.because we again divide it by s,Measure becomes m/s
^{
2
}

#### Example 1

**
A car is moving at a speed of 6 meters/Second
**

**
In 5 Seconds, he increases its speed to 16 meters /second
**

**
What is Acceleration
**

Initial Velocity = u = 6

Final Velocity = v = 16

Time Taken = t = 5

Acceleration=Increase in Velocity/Time Taken

a = (Final Velocity - Old Velocity)/Time Taken

a = (v - u)/t

a = (16 - 6)/5

a = (10)/5

a = 2 Meters/Second
^{
2
}

#### Example 2

**
A car Is stationary
**

**
In 5 Seconds,it reaches its speed to 16 meters /second
**

**
What is Acceleration
**

Because,Car is Stationary,Its initial velocity = 0

So u = 0

V = 16

Acceleration = Increase in Velocity/Time Taken

a = (Final Velocity - Old Velocity)/Time Taken

a = (v - u)/t

a = (16 - 0)/5

a = (16)/5

a = 3.2 Meters/Second
^{
2
}

#### Negative Acceleration

Sometimes,acceleration of a body decreases

Example

Speed of car decreases

This is called negative acceleration or Retardation

#### Example 3

**
A car is running at a speed of 30 meters/second
**

**
It applies brake and reaches speed of 22 meters per second in 2 Seconds
**

**
What is acceleration
**

Initial Velocity = u = 30

Final Velocity = v = 22

Time Taken = t = 2

Acceleration=Increase in Velocity/Time Taken

a = (Final Velocity - Old Velocity)/Time Taken

a = (v - u)/t

a = (22 - 30)/2

a = -8/2

a = -4 Meters/Second
^{
2
}

So in this case,there is Acceleration of -4 Meters/Second
^{
2
}

We can say that there is Negative Acceleration of 4 Meters/Second
^{
2
}

Note

Negative Acceleration or Retardation of 4 Meters/Second^{ 2 }

Note: Negative Acceleration is also called retardation

##

Questions

**
Q 1 Page 103 -
**
When will you say a body is in

(i) uniform acceleration? (ii) nonuniform acceleration?

**
Q 2 Page 103 -
**
A bus decreases its speed from 80 km h–1 to 60 km h–1 in 5 s. Find the acceleration of the bus.

**
Q 3 Page 103 -
**
A train starting from a railway station and moving with uniform acceleration attains a speed 40 km h–1 in 10 minutes. Find its acceleration

**
NCERT Question 9 -
**
State which of the following situations are possible and give an example for each of these:

**
Example 8.4 -
**
Starting from a stationary position, Rahul paddles his bicycle to attain a velocity of 6 m s–1 in 30 s. Then he applies brakes such that the velocity of the bicycle comes down to 4 m s-1 in the next 5 s. Calculate the acceleration of the bicycle in both the cases.