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I've been reading the Feynman Lectures on Physics and I've stumbled on something. I understand the theory but not how they arrived at the answer. It's to do with firing a bullet from a gun and working out the speed it would need to travel in a curve around the earths surface in order to be at the same height that it started out. They prove it using plane geometry which has confused me because as far as I understand it the bullet would need to travel in an arc for which ultimately the equation will need an angle. The answer is about 5 miles a second. Please can someone explain to me how they would approach this problem assuming that the raduis of the earth is 4000miles and the an object will fall 16ft/sec under the influence of gravity?

Thanks

Mark

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# Newton's Law of Gravitation Feynman Lectures

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