# London into Australia in 90 minutes

Me and my friend are having a debate on whether it would be possible for a human to travel at 15,000 miles an hour from London to Australia in the matter of 90 minutes. Would a human be able to survive travel in such at fast speeds knowing he will have to overcome immense amount of g's. Basically is it possible for a human? or will he suffer death in the process?

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Think ICBM. Think the Mercury launches. Or as Heinlein called it "semi-ballistic". –  dmckee Feb 3 '13 at 2:17
G-forces have nothing to do with high speeds. G-forces have to do with acceleration--with changing speeds. I don't think this question is really about how fast someone's going. Rather, it's about how they get going that fast. What kind of acceleration mechanism do you have in mind? –  Muphrid Feb 3 '13 at 6:11
Concerning radial acceleration, you needn't worry about leaving your seat. Only at speeds of roughly 17,686 mph along the earth's (assumed smooth) surface will you become "weightless". And only at 25,012 mph you will experience -1 G while stuck to the roof of your vehicle. Above 30,633 mph you might want to sit upside down, because otherwise you will potentially experience redout and death. –  Glen The Udderboat Feb 3 '13 at 22:30

The distance from London to Australia is about 17,000km. If you wanted to minimise the acceleration you'd feel during the trip you'd accelerate continuously for the first half of the journey (8,500km) then decelerate at the same rate for the second half. To work out what acceleration is required you use the SUVAT equation:

$$s = ut + \frac{1}{2}at^2$$

For half the journey the distance $s$ is 8,500km and the time $t$ is 45 minutes (2700 seconds), so using the above equation the acceleration required is about 2.33m/s$^2$, which is only about a quarter of a $g$. The only trouble is that your speed at the halfway point would be about 6,300m/s (about Mach 18), so you'd need a rocket rather than a plane to do it.

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