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20 mph No. The answer isn't 20 mph. You need to consider the speed of the train as well as the speed of the ball. 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 |