Question

A car moving on a straight road covers one third of the distance with $20 \mathrm{~km} / \mathrm{hr}$ and the rest with 60 $\mathrm{km} / \mathrm{hr}$. The average speed is (a) $40 \mathrm{~km} / \mathrm{hr}$ (b) $80 \mathrm{~km} / \mathrm{hr}$ (c) $46 \frac{2}{3} \mathrm{~km} / \mathrm{hr}$ (d) $36 \mathrm{~km} / \mathrm{hr}$

Name: Problem 11, Chapter 2: Genius Physics (Class 11) - For IIT-JEE and CBSE
Uploaded: 2022-03-06T15:32:35-08:00
Duration: 1 min 46 s
Channel: Saman Zulfiqar
Description: A car moving on a straight road covers one third of the distance with 20 km / hr and the rest with 60 km / hr. The average speed is (a) 40 km / hr (b) 80 km / hr (c) 46 (2)/(3) km / hr (d) 36 km / hr

   A car moving on a straight road covers one third of the distance with $20 \mathrm{~km} / \mathrm{hr}$ and the rest with 60 $\mathrm{km} / \mathrm{hr}$. The average speed is
(a) $40 \mathrm{~km} / \mathrm{hr}$
(b) $80 \mathrm{~km} / \mathrm{hr}$
(c) $46 \frac{2}{3} \mathrm{~km} / \mathrm{hr}$
(d) $36 \mathrm{~km} / \mathrm{hr}$

Genius Physics (Class 11) - For IIT-JEE and CBSE

Pradeep Kshetrapal 1st Edition

Chapter 2, Problem 11

Instant Answer

Solved by Expert Saman Zulfiqar

03/06/2022

Step 1

According to the problem, the car covers one third of the distance with a speed of $20 \mathrm{~km/hr}$ and the rest with a speed of $60 \mathrm{~km/hr}$. So, the distances covered at these speeds are $\frac{d}{3}$ and $\frac{2d}{3}$ respectively. Show more…

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A car moving on a straight road covers one third of the distance with $20 \mathrm{~km} / \mathrm{hr}$ and the rest with 60 $\mathrm{km} / \mathrm{hr}$. The average speed is (a) $40 \mathrm{~km} / \mathrm{hr}$ (b) $80 \mathrm{~km} / \mathrm{hr}$ (c) $46 \frac{2}{3} \mathrm{~km} / \mathrm{hr}$ (d) $36 \mathrm{~km} / \mathrm{hr}$

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Key Concepts

Average Speed

Average speed is defined as the total distance traveled divided by the total time taken to travel that distance. It is an overall measure that captures the effect of varying speeds over different segments of a journey, providing a single value that summarizes the rate of motion.

Distance-Time Relationship

The distance-time relationship is expressed by the formula time = distance ÷ speed. This fundamental relation allows calculation of the time taken for each segment of a journey when the distances and respective speeds are known, which is then used to determine the average speed.

Harmonic Mean

The harmonic mean is a type of average used especially when dealing with rates. In scenarios where equal distances are covered at different speeds, the harmonic mean gives the correct average speed because it appropriately accounts for the reciprocal nature of speed with respect to time.

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