## Chapter No.2

## Kinematics

### Table of content:-

Number of topics | Name the topics |

1 |
Kinematics |

2 | Chapter within short Questions |

3 | Exercise Short Questions |

4 | Answer the Question |

5 |

### ( Chapter within short Questions)

##### Q.1 when a body is said to be at rest?

Ans. When a body does not change its position with respect its surroundings. It is said to be in the state of rest.

##### Q.2 Give an example of a body at rest and is in motion at some time?

Ans. Whether a person is sitting in a car; he will be in the state of rest with respect to the other person sitting in the car he will be in the state of motion with respect to the person standing the road side at the same time.

##### Q.3 Mention the type of motion in each of the following?

###### (i) A ball moving vertically upward.

Ans. Linear motion ( translatory motion)

###### (ii) A child moving down a slide.

Ans. Linear motion ( translatory motion)

###### (iii) Movement of a player in a football ground.

Ans. Random motion ( translatory motion)

###### (iv) The flight to a butterfly.

Ans. Random motion ( translatory motion)

###### (v) An athlete running in a circular track.

Ans. Circular motion ( translatory motion)

###### (vi) The motion of a wheel.

Ans. Rotatory motion

###### (vii) The motion of a cradle.

Ans. Vibratory motion

Textbook exercise

###### Q.1 Explain Translatory motion and give examples of various types of Translatory motion?

Ans. See Q.1 long question

###### Q.2 Differentiate between them?

###### Ans. (i)Rest and motion

###### Rest:

A body is to be at rest if it does not change its position with respect to its surroundings e.g a book lying on tha table.

###### Motion:

A body is said to be in motion if it. Change its position with respect to its surroundings. E.g. a car moving on a road.

###### (ii) Difference between Circular motion and Rotatory motion

###### Circular motion:

The motion of an object in a circular path is known as circular motion.

**Examples:**

- Around the sun motionElectron
- moving around nucleus.
- Moon motion around the earth.
- A car moving in a circular track.

###### Rotatory motion:

The spinning motion of a body about its axis is called rotatory motion.

**Examples:**

- Wheel motion about its axis.
- Spinning motion top about its about its axis.
- Earth motion about its geographic axis.

###### (iii) Difference between Distance and Displacement

###### Distance:

The length of path between two points is known as distance.

- It can be discribe completely by its magnitude only
- It is a scalars quantity
- It is repersented by “S”
- Its SI units is meter(m)

###### Displacement:

The shortest distance between two points which have Both magnitude direction known as displacement.

- It can be described completely by magnitude and direction.
- It is a vector Quantity
- It is repersented by”d”
- Its SI units is meter (m)

###### (iv) Difference between speed and velocity

###### Speed:

The distance between covered in unit time is known as speed

- Its represented by letter “V”.
- Speed can be completely describe by its magnitude only.
- Speed is a scalar quantity
- SI unit of speed is ms-1
- Speed is related to distance covered by body and time taken.

###### Velocity:

The rate of change of displacement of a body is called velocity.

Velocity= displacement/time

V=d/t

- Velocity can describe completely by its magnitude and direction.
- It is a vector Quantity
- SI unit of velocity is ms-1
- Velocity is related to displacement covered by a body and time taken.

###### (v) Difference between scalar and vector.

###### Scalar:

They are completely describe by their magnitude only. It can be added by simple mathematical rules.

Example:- speed, distance, time, mass, length, temperature etc.

###### Vector:

physical Quantities which are completely describe by their magnitude and direction as well are known as vector Quantities. Vector can be added by graphical method known as head to tail rule.

**Example**: force, displacement, torque, momentum, acceleration, velocity etc.

##### Q.3 Define the term speed, velocity, and acceleration?

###### Ans. Speed:

The distance covered by an object in unit time is called speed.

Mathematical formula

Speed= distance covered/ total time

Speed= S/t

Distance=Speed × time

S=v×t

It is a scalar quantity

###### Velocity:-

The rate of displacement of a body with respect to time is called velocity.

Mathematical

Velocity= displacement/time taken

V=d/t

d=V×t

It is a vector Quantity.

###### Acceleration:

The rate of change of velocity of a body is known as acceleration.

How velocity changes:-

Velocity of the body change due to change either in magnitude or direction or both.

Mathematical form

Acceleration=change in velocity/total time

Acceleration=final velocity – intial velocity/total time

aav= vf – vi/t

Its SI units meter per second per second ( ms-3 )

It is a vector Quantity.

###### Q.4 Can a body moving at a constant speed have acceleration?

Ans. A body is moving with constant speed many or may not have acceleration.

• If a body is moving with constant speed in straight line does not have acceleration.

• If a body is moving with constant speed and is not moving in straight line have acceleration.

##### Q.5 How do riders in a Ferris Wheel possess translator motion but not rotatory motion?

Ans. Rider moving in a Ferris Wheel are in trans partitional motion but not posses rotatory motion. Because their motion is in a circle with out rotation.

##### Q.6 Sketch a distance time graph for a body starting from rest. How will you determine the speed of a body from this graph?

Ans. The distance time graph is shown below. The slop of the, graph gives speed with the help of the

Formula:-

Speed of the object= slope of line AB

##### Q.7 What would be the shape of speed time graph of a body moving with variable speed?

Ans. The shape of the speed time graph is zigzag( not a straight line) when the body has variable speed.

##### Q.8 Which of the following can obtained from speed time graph of a body?

(i) initial speed

(ii) final speed

(iii) distance covered on time t

(iv) acceleration of motion

Ans. From speed time graph we can calculate initial speed, final speed, distance covered in time t and acceleration of motion.

##### Q.9 How can vector Quantities represented graphically?

Ans. A vector can be represented graphically by drawing a straight line with an arrow head at one end. The lenght of the line tells the magnitude and arrow head shows the direction of the vector. A•••••••>B

##### Q.10 Why vector Quantities cannot added and subtracted like scalar quantities?

Ans. In addition of vectors, both magnitude and direction are involved. Vectors cannot added by simple method of scalar addition vector. It can added by graphical method known as head to tail rule.

##### Q.11 How are vector Quantities important to us in our daily life?

Ans. It would be meaningless to describe vector without direction. For example, distance of a place from reference point is insufficient to locate that place. This direction of that place from reference point is also necessary to locate it.

##### Q.12 Sketch a velocity time graph for the motion of the body. From the graph explaining each step, calculate total distance covered by the body?

Ans. Total distance travelled= area under the graph ( trapezium OABC)

=1/2(sum of parallel sides)× height

=1/2(18s+30s)×16ms-1

=384m