Exercise

I. 

1. 

Ans: uniform motion

2. 

Ans. periodic motion

3. 

Ans: km/h

4. 

ans: distance travelled ➗ time taken

5. 

Ans: in non uniform motion

6.

Ans: 8 pm

II.

1

Ans: Obelisk is a tall, four sided carved pillar which helped people to know time.

2. 

Ans: One complete movement of a pendulum is called an oscillation.

3

Ans: Quartz is a mineral found in Earth's crust.

4.

Ans: The two methods of writing time are: 12 hour method and 24 hour method

5. 

Ans: The SI unit of time is second.

6.

Ans: When an object changes its position with time, it is said to be in motion.

7.

Ans: Types of motion are:

  • Linear
  • circular
  • periodic
  • rotational
  • oscillatory
  • vibratory
8.

Ans: A speedometer measures the speed of a vehicle in motion.

III.

1

Ans: The distance travelled by an object in unit time is the speed of the object. It is calculated by using the following formula

Speed = Distance ÷ Time

2.

Ans: An atomic clock is used to maintain the accurate standard time of a nation. The atomic clock works on radiation emitted by a cesium atom.

3.

Ans: The speed of an object in motion depends on two factors:

  • The total distance travelled
  • the total time taken to travel the distance.
4. 

Ans: Odometer records the distance travelled by an object. Odometer is a single wheeled device. As the wheel rolls a meter attached to the wheel records the distance the wheel has travelled.

5.

Ans: Uniform motion: Uniform motion covers equal distance at an equal time interval.

Non-uniform motion: Non-uniform motion covers unequal distance at equal time interval.

IV.

1. 

Ans: In a quartz watch, a tiny bar - shaped quartz crystal is placed in an electronic circuit. An electronic cell attached to the circuit makes the crystal oscillate with an accurate frequency. The oscillations are translated by a tiny computer chip into pulses. The pulses drive a miniature motor which turns gears that move the watch's hands. This is how a quartz watch works.

2. 

Ans: Speedometer:- Speedometer measures the speed of an vehicle in motion.

Odometer:- Odometer measures the distance covered by a vehicle.

3.

Ans: A motion that repeats itself after equal intervals of time is known as periodic motion. Example:- The revolution of our earth is an example of periodic motion. Because our earth is repeatedly revolving around the sun in the same path and in a period of 365 days approximately.

4. 

Ans: The two methods of writing time are as follows.

12-hour method:- In this method tume is written with the help of certain rule. Time is also written with the abbreviations a.m. and p.m. To indicate the time from midnight to noon a.m. is used while to denote time between noon to midnight p.m. is used.

24-hour method:- In this method the time is noted continuously from 1 - 24 hours and is written without any abbreviations. The midnight is indicated by 00:00.