# Kinematics

## 9th Class Physics Chapter 2 Exercise Short Questions with Answers

**Q 2.2 : Explain translatory motion and give examples of various types of translatory motion .**

**Translatory Motion :**

” The motion in which a body moves along a line (straight or curved ) without any rotation , is called translatory motion .”

**Types of Translatory Motion :**

- Circular motion
- Linear motion
- Random motion

**1 . Circular Motion :**

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

**Example : **A car moving along a circular track .

**2 . Linear Motion :**

” Straight line motion of a body is known as linear motion .”

**Example :** Aero-plane flying straight in the air is linear motion .

**3 . Random Motion :**

” The disordered or irregular motion of an object is called random motion .”

**Example :**Motion of insects and birds is random motion .

**Q 2.3 :Differentiate between the following .**

**i .**

Rest | Motion |

→A body is said to be at rest , if it does not change its position with respect to its surroundings . | → A body is said to be in motion , if it changes its position with respect to its surroundings . |

Example | Example |

→A passenger sitting in a moving bus is at rest because he \ she is not changing his\her position with respect to other passengers or objects in the bus . | →To an observer outside the moving bus , the passenger and the other objects inside the bus are in motion . |

**ii.**

Circular Motion | Rotatory Motion |

→The motion of an object in a circular path is known as circular motion . | →The spinning motion of a body about its axis is called its rotatory motion . |

→In circular motion , the point about which a body goes around is outside the body . | →In rotatory motion , the line around which a body moves about is passing through the body itself . |

Example | Example |

→Motion of earth around the sun .→A toy train moving in a circular track. | →Motion of earth about its geographical axis .→Motion of top around its axis . |

**iii.**

Distance (S) | Displacement (d) |

” Total length of a path between two points is called distance between these two points .” | “The shortest distance between two points is called displacement .” |

→Distance is a scalar quantity . | →Displacement is a vector quantity. |

**iv.**

**v.**

Linear Motion | Random Motion |

” Motion of a body along a straight line is called linear motion .” | ” The disordered or irregular motion of an object is called random motion .” |

Example | Example |

Free falling object | Motion of gas molecules |

**vi.**

Scalers | Vectors |

“A scaler quantity is described completely by its magnitude .” | ” A vector quantity is described completely by its magnitude and direction .” |

Example | Example |

Mass , Length , time , speed , volume , work , energy | Velocity , force , displacement , motion , torque |

**Q 2.4 : Define the term speed , velocity and acceleration .**

**Speed (v):**

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

**Velocity (v) :**

” The rate of change of displacement is called velocity .”

**Acceleration (a) :**

**Q 2.5 : Can a body moving at a constant speed have acceleration .**

**Yes** , A body moving at a constant speed have acceleration .

**Condition :**

If a body is changing its direction then it has acceleration acting towards Centre provided by centripetal force .

**Q 2.6 : How do riders in a Ferris wheel possess translatory motion but not rotatory motion ? **

Riders in Ferris wheel have circular motion (a type of translatory motion ).

**Reason :**

- Because their motion is in a circle without rotation .
- And the line about which wheel riders goes around , lies outside the body .

**Q 2.7 : Sketch a distance-time graph for a body starting from rest . How will you determine the speed of a body from this graph ?**

**Q 2.8 : What would be the shape of a speed-time graph of a body moving with variable speed ?**

The shape of velocity-time graph is zigzag i.e., not a straight line , when the body is moving with variable speed .

**Q 2.9 : Which of the following can be obtained from speed-time graph of a body ?**

**i . Initial speed **

**ii . Final speed **

**iii . Distance covered **

**iv . Acceleration of motion **

All the above quantities can be obtained from speed-time graph of a moving body .

**Q 2.10 : How can vector quantities be represented graphically ?**

**Graphical representation of Vector :**

Graphically , a vector can be represented by a line segment with an arrow head .

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**Q 2.11 : Why vector quantities cannot be added and subtracted like scalar quantities ?**

**v**ector quantities cannot be added and subtracted like scalar quantities.

**Reason : **Vector quantities have direction and quantities having direction cannot be added and subtracted like scalar quantities .

**Q 2.12 : How are vector quantities important to us in our daily life ?**

Vector quantities are very important to us in our daily life .

- Vector quantities help us to determine position / direction of any place .

**Example :** Pilots use vectors to detect their destination .

**Q 2.13 : Derive equations of motion for uniformly accelerated rectilinear motion .**

**Q 2.14 : sketch a velocity-time graph for the motion of the body . From the graph explaining each step , calculate total distance covered by the body .**

- The area under a speed-time graph represents the distance travelled by the object (i.e. car ) .

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