This video presents a classic kinematics puzzle: if you travel from point A to point B at 60 km/h, what speed must you travel back to achieve an average speed of 120 km/h for the entire round trip? The intuitive answer of 180 km/h is incorrect. Using the formula speed = distance/time, the time taken for the first leg equals the time for the entire round trip, meaning you would need to travel instantaneously (infinite speed) to achieve this average. This demonstrates that average speed for a round trip cannot simply be doubled by doubling the return speed, as the time spent traveling in each direction affects the overall average.
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Can You Outsmart Einstein in this Easy Question?Added:
You will fall for this intuition question, just like Einstein almost did.
And it's quite simple. Imagine you're driving a car at 60 km/h from point A to point B. At what speed do you need to travel back to point A such that your average speed for the entire two-way journey is 120 km/h. Pause to think about it. It's not 180 km/h. The formula is speed equals distance over time. For the first journey, we traveled a distance of X at 60 km/h. So, let's sub all these values into the formula. And let's say the time is T1. For the full two-way journey, you travel 2X at 120 km/h. And let's say time is T2. But, we can divide by two on both sides, leaving us with 60 equals X over T2, which is identical to the first journey, meaning that T1 and T2 should be exactly the same. What this means is that the time taken to go from point A to point B is the same as the entire two-way journey.
In other words, you would need to instantly go from point B to A to make the average velocity 120 km/h. And that's why that
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