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Note on Acceleration and Retardation

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Acceleration

Acceleration is defined as the change in velocity per unit time. Acceleration is measured in m/s2.

=

Retardation

The negative acceleration is called retardation or deceleration. Its unit is same as acceleration.

Example:

1. Car starts from rest. After 5 seconds, its velocity becomes 10 m/s. Then find its acceleration.

Initial velocity (u) = 0

Final velocity (v) = 10 m/s

Time taken (t) = 5 s

Acceleration (a) =?

Or,

Or,

∴ a = 2m/s2

2. The Car which starts from the rest has an acceleration of 0.3 m/s2. After 1 minute what will be its acceleration? What is the distance travelled by car?

Initial velocity (u) = 0

Time taken (t) = 1 min= 1 × 60 s = 60 s

Acceleration (a) = 0.3 m/s2

Final velocity (v) =?

Distanced travelled (s) =?

According to formula, v= u+ at

Or, v = 0 + 0.3 × 60

V= 18 m/s

∴ s =540 m

 

Equation of motion of uniform acceleration

Equations involving displacement, initial velocity, final velocity, acceleration and time of the motion of a moving body are equations of motion.

Considering a body moving in a straight line with uniform acceleration is shown in the figure.

Let,

Displacement = s

Initial velocity = u

Final velocity = v

Acceleration = a

Time taken = t

Relation between u, v, a and t

 

 

 

Or,

Or, at = v-u

∴ v= u + at ………….. (i)

This is the first equation of motion.

Relation between u,s, v and t

Or,

Or, \(\text{Average Velocity}=\frac{\text{Total Displacement(s)}}{\text{Total Time Taken(t)}}\)

Or,

 

 

As both, equation is equal

Or,

Or, 2s = (u + v)t

……………… (ii)

This is the second equation of the motion.

 

Relation between s, u, a and t

We already have,

V= u + at………….. (i)

s = (u + v)t…………… (ii)

Putting value of v from equation (i) in (ii)

Or,

Or, s =

Or, s = 2u×t + at × t× ½

∴ s = ut + ½ at2………………. (iii)

This is the third equation of motion.

  • Acceleration is defined as the change in velocity per unit time. Acceleration is measured in m/s2.
  • The negative acceleration is called retardation or deceleration. Its unit is same as acceleration.
  • Equations involving displacement, initial velocity, final velocity, acceleration and time of motion of a moving body are equations of motion.
 
.

Very Short Questions

Acceleration is defined as the change in velocity per unit time. Acceleration is measured in m/s2.

Solution

Initial velocity (u) = 0

Final velocity (v) = 10 m/s

Time taken (t) = 5 s

Acceleration (a) =?

Or,

Or,

∴ a = 2m/s2

Solution:

Initial velocity (u) = 0

Time taken (t) = 1 min= 1 × 60 s = 60 s

Acceleration (a) = 0.3 m/s2

Final velocity (v) =?

Distanced travelled (s) =?

According to formula, v= u+ at

Or, v = 0 + 0.3 × 60

V= 18 m/s

∴ s =540 m

Solution:

Or,

Or, at = v-u

∴ v= u + at ………….. (i)

This is the first equation of motion.

Or,

Or,

Or,

As both, equation is equal

Or,

Or, 2s = (u + v)t

……………… (ii)

This is the second equation of the motion.

Solution:

V= u + at………….. (i)

s = (u + v)t…………… (ii)

Putting value of v from equation (i) in (ii)

Or,

Or, s =

Or, s = 2u×t + at × t× ½

∴ s = ut + ½ at2………………. (iii)

This is the third equation of motion.

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  • Negative accelration is called ______.

    retardation


    deduction


    induction


    reduction


  • Velocity of car cannot be changed by ______.

    Changing the direction


    changing speed and direction


    Keeping speed and direction constant


    changing the speed


  • 'Each and every action has its equal and opposite reaction.' Which law of motion is it?

    4th law


    2nd law


    3rd law


    1st law


  • When a ball bounces off a wall, which law of Newton's Motion does it follow?

    4th law
    2nd law
    1st law
    3rd law
  • When a tablecloth of a table with a plate is swiftly pulled and a plate remains intact in its position which law of Newton's Motion does it follow?

    3rd law
    2nd law
    4th law
    1st law
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DISCUSSIONS ABOUT THIS NOTE

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Dinesh

A car starts with an velocity of 72 km/hr and stops after 4sec' how far does the car move?


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ek Rana

a vehicle was at a speed of 90 km/h. on seeing a baby 20 m ahed oon the road, the driver jammed on the breaks and it came to rest at a distance of 15 m. what is its retardation and how long does it take to come at rest?


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