__ Chapter -2 Motion__

__Chapter -2 Motion__

__SHORT ANSWER TYPE__:

**1. Comment on the statement 'rest and motion are relative terms. Give an examp**le.

**Ans**- The statement "rest and motion are relative terms" means that whether an object is at rest or in

__ Example__: Consider a passenger sitting inside a moving train:- The passenger is at rest with respect to

The passenger is in motion with respect to train because the train is moving relative to the ground, and

hence the passenger is also moving with it.**2. Fill in the blanks using one of the words: at rest, in motion.**

(a) A person walking in a compartment of a stationary train is __rest__ relative to the compartment and is

__rest__relative to the platform

(b) A person sitting in a compartment of a __moving__ train is rest relative to the other person sitting by his side and is __motion__ relative to the platform.

**3. Name five different types of motion you know.**

**Ans**: Types of motion -1. Translatory motion

2. Rotatory motion

3. Circular motion

4. Oscillatory motion

5. Vibratory motion

6. periodic motion

7.Non periodic motion

**4. What do you mean by translatory motion ? Give one example.**

**Ans: **A body said to have translatory motion if every point on a moving body moves through the same

*Example:* motion of Apple falling vertically down

**5. What is rotatory motion? Give two examples.**

**Ans**: When a body moves about to fixed point, the body said to have rotatory motion.

*Example*: motion of ceiling fan

**6. What is meant by circular motion? Give one example.**

**Ans**: If a body moves in a circular path the motion is said to be circular motion.

Example-motion of Satellite around the earth.

**7. How does rotatory motion differ from circular motion?**

**Ans-**__Rotatory Motion__**:** The axis of rotation is within the object.

__Circular Motion__**: **The axis of rotation is outside the object, at the center of the circular path.

* Rotatory Motion*: Different points in the object move in concentric circles around the axis.

__Circular Motion__: The object as a whole moves along a single circular path

**8. What is vibratory motion? Give one example.**

**Ans**: The to and fro motion of a part of the body keeping its rest part fixed is called vibratory motion.

*Example*: Our vocal cords vibrate to produce sound when we speak or sing.

**9. What is random motion? Give an example.**

**Ans**: The motion of an object which takes path in no specific direction is called random motion.

*Example*: Motion of molecules of a gas.

**10. Name the type/types of motion being performed by each of the following:**

(a) Vehicle on a straight road- **Rectilinear **

(b) Blades of an electric fan in motion - **Rotatory **

(c) Pendulum of a wall clock- **Oscillatory **

(d) Smoke particles from chimney-: **Random**

(e) Hands of a clock- **Circular**

(f) Earth around the sun - **Circular**

(g) A spinning top.- **Rotatory**

**11. State the types of motion of the following:**

(a) The needle of a sewing machine- **periodic**

(b) The wheel of a bicycle- **Translatory and Rotatory **

(c) The drill machine-**Translatory and Rotatory **

(d) The carpenter's saw- **Translatory and Oscillatory.**

**12. Define the term weight and state its S.I. unit.**

**Ans:** The weight of a body on Earth is the force with which Earth attracts the body. Its SI unit is newton ( N )

**13. How are the units of weight, kgf and newton related ?**

**Ans:** 1 kgf = 9.8 N

**14. Which quantity: mass or weight, does not change by change of place?**

**Ans:** Weight changes from place to place.

**15. State which of the quantities, mass or weight is always directed vertically downwards.**

**Ans:** Weight is always directed vertically downwards.

**C. LONG ANSWER TYPE QUESTIONS**:

**1. Explain the meaning of the terms rest and motion.**

**Ans:** A body said to be at rest ,if he does not change its position with respect to its immediate

A body said to be in motion, if it changes its position with respect to its immediate surroundings.

**2. Explain the meanings of (i) rectilinear motion, and (ii) curvilinear motion. Give one example of**

**each.**

**Ans**: __ Rectilinear motion__: the motion of a body in a straight line is called linear motion.

*Example *- A ball is dropped, falling vertically down.

__ Curvilinear motion__: the motion of a body in a curved path is called curvilinear motion.

*Example*: The motion of a cycle while taking a turn on the road

**3. Explain oscillatory motion by giving one example.**

**Ans**: The to and fro motion of a body from its rest position is called the oscillatory motion for example

**4. Differentiate between periodic and non-periodic motions by giving an example of each.**

**Ans**: __ Periodic motion__- A motion which gets repeated after regular interval of time is called Periodic

__ Non periodic motion__ - The motion which does not repeat itself after a regular interval of time is called

**5. Give two examples to illustrate that a body can have two or more types of motion**

**simultaneously.**

**Ans**: 1. * A car Wheel*:

The wheel rotates around its own axis as it rolls.__Rotational Motion__:Simultaneously, the wheel moves forward along a surface.__Translational Motion__:

2.

*Earth around the Sun*:

The Earth spins around its axis, resulting in day and night.__Rotational Motion__:The Earth simultaneously moves around the Sun__Circular Motion__:

**6. Distinguish between uniform and non-uniform motion, giving an example of each.**

**Ans**:

**Example**:

*Uniform motion*: Car moving at a constant speed on a highway.

*Non*-

*Uniform motion*: Car again moving after halt of 5 minutes.

**7. How do you determine the average speed of a body in non-uniform motion ?**

**Ans**: Average speed= Total distance÷ total time taken

8. State two differences between mass and weight.

Feature | Mass | Weight |
---|

Device | Beam balance | Spring balance |

Units | kilogram (kg) | newton (N) |

__NUMERICALS__:

A car covers a distance of 160 km between two cities in 4 h. What is the average

speed of the car ?Answer:Distance =160 km

Time taken = 4h

Speed = ?

Speed = Distance covered / Time taken

= 160km / 4h = 40 km h-1

#### Question 2:

A train travels a distance of 300 km with an average speed of 60 km h_1. How

much time does it take to cover the distance?Answer:Speed = 60 km h-1Distance covered = 300 km

#### Question 3:

A boy travels with an average speed of 10 m s-1 for 20 min. How much distance

does he travel ?Answer:Average speed of boy = 10 m s-1Time taken = 20 min

Distance travelled = Speed × Time taken

Convert minutes into seconds

1 minute = 60 sec.

20 minutes = 20 × 60 = 1200 sec.

Distance travelled = 10 m s-1 × 1200 sec.

= 12000 m Or 12 km

#### Question 4:

A boy walks a distance 30 m in 1 minute and another 30 m in 1.5 minute. Describe

the type of motion of the boy and find his average speed in m/sAnswer:As the speed does not remain constant throughout the journey the motion is non-uniform

Total distance travelled in going and coming back

d = 30 m + 30 m = 60 m

Total time taken in going and coming back

t= 2.5 min = 2.5 x 60 s = 150 s

Average Speed = total distance ÷ total time

= 60 m x 150 s = 900 m/s

#### Question 5:

A cyclist travels a distance of 1 km in the first hour, 0.5 km in the second hour and

0.3 km in the third hour. Find the average speed of the cyclist in(i) km h-1, (ii) m s-1Answer:

(a) Distance travelled in first hour = 1 km

Distance travelled in second hour = 0.5 km

Distance travelled in third hour = 0.3 km

Total time taken = 3 h

Total distance travelled = 1 + 0.5 + 0.3 = 1.8 km

Average Speed= Total distance ÷ Total time

= 1.8 km ÷ 3 h = 0.6 km/ h = 0.6 x 5/18 m/s = 0.167 m/s

#### Question 6:

A car travels with speed 30 km h-1 for 30 minute and then with speed 40 km h-1 for one hour. Find :

(a) the total distance travelled by the car

(b) the total time of travel, and

(c) the average speed of car

Answer:

Speed of car for first 30 minutes = 30 km h-1

Distance covered in 30 min 15 km

Speed of car for next 1 hour = 40 km h-1

Distance covered in 1 hr = 40 km

(a) Total distance travelled by the car = 55 km

b) Total time taken= 1,5 h

c) Average speed = Total distance ÷ Total time

= 55 km÷ 1.5 h = 36.67 km/ h

#### Question 7:

On earth the weight of a body of mass 1.0 kg is 10 N. What will be the weight of a boy of mass 37 kg in (a) kgf (b) N

Answer:

Weight of a body of mass 1.0 kg body = 10 N

(a) Weight of a boy of mass 37 kg = 35 kgf

(b) Weight of a boy of 37 kg in newton will be 1 kgf = 10N

∴ 37 kgf = 37 × 10 N

= 370 N

**Question 8:**

The weight of a body of mass 6.0 kg on moon is 10 N. If a boy of mass 30 kg goes from earth to the moon surface, what will be his (a) mass, (b) weight ?

Answer:(a) Mass remains same it does not change

So mass of boy 30 kg on earth = 30 kg on moon surface

(b) Weight of mass of 6 kg on moon = 10 N

__Check out this mind map on motion__: Rainbow mindmap of Motion

__Check out this video on YouTube__: