Discover the Answer to This Mind-Boggling Riddle About Average Speeds

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Homework Help Overview

The discussion revolves around calculating the average speed of a car traveling to a destination at different speeds for the outbound and return trips. The subject area pertains to average speed and the application of means in physics.

Discussion Character

  • Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the calculation of average speed using different methods, including the harmonic mean and the arithmetic mean. There is a discussion about the common mistake of using the arithmetic mean for this scenario.

Discussion Status

Some participants have provided calculations and insights into the correct approach for finding the average speed, while others reflect on the initial confusion regarding the problem. The conversation appears to be productive, with clarification on the appropriate mathematical method being discussed.

Contextual Notes

Participants acknowledge the potential for misunderstanding the problem setup, particularly in distinguishing between different types of means when calculating average speed.

Tom McCurdy
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You drive a car at a speed of 40 km/hr to a place and then 60 km/hr back... what is the average speed of the car.

I feel really stupid for asking this but its really making me mad..
 
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hahaha as soon as i posted it it was so obvious...

Set distance equal to one

t1=1/40 t2=1/60

[tex]\frac{\Delta d}{\Delta t}=avg vel[/tex]

[tex]\frac{2}{\frac{1}{40}+\frac{1}{60}}[/tex]
 
Which produces 48 km/hr as answer
 
You are correct. Often people make the obvious mistake to take the arithmetic mean, being (40+60)/2 = 50 but in this case, you need the harmonic mean :smile:
 
[tex]\frac{2}{\frac{1}{40}+\frac{1}{60}}[/tex]
harmonic mean could be calculated slightly easier:
[tex]\frac{v_1 v_2}{\frac{v_1 + v_2}{2}}[/tex]
 
Last edited:

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