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30 mph No. The answer isn't 30 mph. You must have subtracted the speed of the ball from the speed of the train. Remember, the ball is moving in the same direction as the train. Try again. Sagan on Time Travel | Traveling Through Time Timespeak | Think Like Einstein | Resources Teacher's Guide | Transcript | Site Map Editor's Picks | Previous Sites | Join Us/E-mail | TV/Web Schedule About NOVA | Teachers | Site Map | Shop | Jobs | Search | To print PBS Online | NOVA Online | WGBH © | Updated November 2000 |