# NCERT Class 9 Science Chapter 4 Describing Motion Around Us Solutions: In-Text and Exercise Questions Explained | SwaVid

This document provides questions and step-by-step solutions for Chapter 4, "Describing Motion Around Us," from the new rationalised NCERT Class 9 Scienc...

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# Describing Motion Around Us

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## Related chapters

Chapter 4 · Class 9 Science

This document provides questions and step-by-step solutions for Chapter 4, "Describing Motion Around Us," from the new rationalised NCERT Class 9 Science textbook, "Exploration."

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In-text Questions

Answer: The distance to maintain from the truck ahead to avoid a collision depends on factors like your speed, reaction time, and braking capabilities. A common practical guideline is the 'three-second rule'. More precisely, it is the sum of the reaction distance and the braking distance.

This question encourages critical thinking about real-world application of motion concepts.

End-of-Chapter Exercise (Revise, Reflect, Refine)

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- The safe distance to maintain from a vehicle ahead depends on several factors, including the speed of your vehicle, the reaction time of the driver, and the braking efficiency of the vehicle and the road conditions.
- A common rule of thumb for safe following distance is the 'three-second rule' (or 'two-second rule' in some contexts), which suggests maintaining a distance that takes at least three seconds to cover. This allows for reaction time and braking distance.
- The actual distance can be calculated using kinematic equations, considering the initial speed, reaction time, and deceleration rate. However, without specific values for these parameters, a precise numerical answer cannot be given.
- In general, the safe distance is the sum of the reaction distance (distance covered during the driver's reaction time) and the braking distance (distance covered while the vehicle is decelerating to a stop).
- Safe Distance = (Speed × Reaction Time) + (Speed² / (2 × Deceleration)).
- NCERT Class 9 Science textbook: Exploration : Chapter 4: Describing Motion Around Us

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