Asked by Cailin
In frozen Minnesota the winter sports carnival includes some unusual events. Since it is dangerous to run on ice, each runner runs on a heavy (240 kg) and long (40 m) wooden plank, which itself rests on the smooth and horizontal ice. One of the competitors is a 60 kg woman who runs the length of the plank in 4.4 seconds, quite an impressive time. Her performance is viewed by a crowd huddled on the ice. The performance that they see is less impressive. With what speed do they see her moving?
Answers
Answered by
bobpursley
consider the log.
the log has to be moving at 60/240 *40/4.4 meters/sec=10/4.5
Consider relativity:
speed runner relative to observer=sr<sub>o</sub>
speed runner relative to log=sr<sub>log</sub>
speed log relative to observer=sl<sub>o</sub>
sr<sub>o</sub>=sr<sub>log</sub>+sl<sub>o</sub>
sr<sub>o</sub>=40/4.4 + (-10/4.4)=30/4.4 m/s
the log has to be moving at 60/240 *40/4.4 meters/sec=10/4.5
Consider relativity:
speed runner relative to observer=sr<sub>o</sub>
speed runner relative to log=sr<sub>log</sub>
speed log relative to observer=sl<sub>o</sub>
sr<sub>o</sub>=sr<sub>log</sub>+sl<sub>o</sub>
sr<sub>o</sub>=40/4.4 + (-10/4.4)=30/4.4 m/s
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