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In the year 2525... (Posted on 2005-03-14) |
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You just landed on the planet Olympus IV, famous for its sports competitions. It's a light planet: the average density is one quarter of the Earths average density. It's also a large planet: the diameter is the double of the Earths diameter. The Olympians are giving a high jump competition, and one crew member takes part. You know that on Earth he jumps 1.98 meters. The record at Olympus IV is 3.86 meters. Should you bet your salary on him winning the competition ?
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Submitted by Hugo
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Rating: 3.0000 (3 votes)
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Solution:
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(Hide)
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The mass is given by the average density multiplied with the volume. The two planets radii stand 1:2, consequently their volumes are 1:8, or their masses are 1/4 x 8. The mass of Olympus IV is 2 times Earths mass.
Gravitation is m x M / R^2 (m = athletes mass, M = planets mass, R is planets radius), so compared to Earth gravitation, at Olymp IV the gravitation is 1/4 (For the radius) x 2 (For the mass difference).
The gravitation on Olympus IV is 0.5 that of the Earth.
So you may expect that he is going to jump two times higher.
But no, he is not going to jump 2 x 1.98 = 3.96 meters.
By jumping he is able to lift his gravitational center 2 times higher then he used to do on Earth. The gravitational center is around one meter from the ground and on Earth he was able to lift that 0.98 meter. Here on Olymp IV he will be able to lift it 0.98 x 2 or 1.96 meter, so he'll jump around 2.96 meter.
I hope you didn't bet on him.
In Eric's comment on the Fosburry Flop, he is in fact giving a better solution than this one. |
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