conflict in "Acceleration: Airbus A380 take off distance."

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Chen Wang

1 mai 2019 10:40

Dear Khan,

In the calculation of how long the runway will have to be for the plane to take off, you mentioned that we use average velocity (0 + 78)/2 times the time 78sec, we get 3042m which is the answer. However, if I use another way: 1+2+3+.....+78=3081m. Why there is such discrepancy? Shouldn't the two ways get the same answer? If I calculate the average velocity using (1+78)/2, then times 78sec, I get 3081m. So could you explain what's wrong? Thanks!

Best regards,

Wang Chen

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Evan Lewis

11 mai 2019 15:11
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Hi Wang Chen,

The two methods you are using can both be represented by the following expressions:

(0 + 78)/2 and (1 + 78)/2

These are clearly not the same expressions. Since the plane started from rest (with a velocity of 0 m/s), the first expression is correct.

Hope this helps!

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