We often state that the speed of light in vacuum is about 3 × 10 8 m s and the average speed of sound in air is about 330 m s . Why do you think the term 'average' is used to describe the speed of sound in the air but not the speed of light in vacuum?

The distance that the sound waves travel in a given amount of time is called the speed of sound. The average speed of sound in the air is about 330 m s . We know that sound waves are mechanical waves, and they can only travel through matter. The speed of sound through dry air at 20 ° C is about 343 m s . The speed of sound may vary through other matter or other temperatures. Since, the speed of sound may vary according to the temperatures and medium, we use the term average to describe the speed of sound. The speed of the light is experimentally found to be constant. Hence, the term average is not required in describing the speed of light.

A bus takes 15 hours to travel from town X and Y and 12 hours to travel from town Y to Z. Calculate the speed of the bus from town 'X' to town 'Y'.

Given that, Distance from X to Y is = 700 km Time taken by the bus from X to Y is = 15 hours = 15 h We know that, Speed = Distance travelled time taken = 700 15 = 46 . 67 km h - 1 Speed of the bus from town 'X' to town 'Y' is 46 . 67 km h - 1 .

A bus takes 15 hours to travel from town X to town Y and 12 hours to travel from town Y to Z. Is the speed of the bus increasing or decreasing from town 'Y' to 'Z' as compared to the speed from 'X' to 'Y'? Find out.

Given that, Distance from town 'X' to town 'Y' is = 700 km Distance from town 'Y to town 'Z' is = 520 km Time taken by the bus from X to Y is = 15 hours = 15 h Time taken by the bus from Y to Z is = 12 hours = 12 h We know that, Speed = Distance travelled Time taken Speed of the bus from town 'X' to town 'Y' is = 700 15 = 46 . 67 km h - 1 . Similarly, speed of the bus from town 'Y' to town 'Z' is = 520 12 = 43 . 3 km h - 1 . Therefore, speed of the bus is decreasing, when it is traveling from town 'Y' to town 'Z'.

A bus takes 15 hours to travel from town X to town Y and 12 hours to travel from town Y to Z. What is the average speed of the bus throughout journey?

Given that, Total distance from town 'X' to town 'Y' and town 'Y to town 'Z' is = 700 km + 520 km = 1220 km Total time taken by the bus from X to Y and Y to Z is = 15 hours + 12 hours = 15 h + 12 h = 27 h We know that, Average speed = Total distance travelled Total time taken = 1220 27 = 45 . 2 km h - 1

Look at the diagram of a simple pendulum. The bob of the pendulum is released at point 'X'. The period of the oscillation is found to be 0 . 25 s . State one measure you can take to ensure that the measurement of the time period of the pendulum is as accurate as possible.

The measurement of the time period of the simple pendulum will be accurate when it oscillates in a vertical plane only. If it is tilted then the oscillations of the pendulum will be affected. While measuring time period start time from the extreme position, because at extreme positions bob of the pendulum momentarily stops.

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WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 1 - Time and Motion>WORKSHEET

Archana Shukla Solutions for Chapter: Time and Motion, Exercise 3: WORKSHEET

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Questions from Archana Shukla Solutions for Chapter: Time and Motion, Exercise 3: WORKSHEET with Hints & Solutions

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WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 1 - Time and Motion>Think Science>Q 1

We often state that the speed of light in vacuum is about $3 \times 10^{8} \frac{m}{s}$ and the average speed of sound in air is about $330 \frac{m}{s}$ . Why do you think the term 'average' is used to describe the speed of sound in the air but not the speed of light in vacuum?