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posted by  radish37 on 11/6/2009 11:57:35 PM  |  status: Live  |  Earned Karma: 50

relative velocity

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N/A N/A N/A N/A 11/7/2009 at 7:00:00 AM
Question Details:
Two twins set out to row separately across a swiftly moving river.  They have identical canoes and can row at the same speed relative to the water.  Twin A heads straight across the river but due to the current, is carried downstream before reaching the oopposite bank.  Twin B heads upstream at an angle of 55o from the bank so as to arrive at hte oppostie bank at a point that is directly across from the starting point.  Determine the ratio of the time it takes twin A to cross the irver to the time it takes twin B to cross.
answer: 0.82
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posted by redcloud173 on 11/7/2009 2:46:42 AM  |  status: Live
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Response Details:
Assume that they both row at a velocity V

after a time t, Twin A has travelled a distance of V*t horizontally across the river (because he headed straight out).  Twin B took a different heading, so his horizontal velocity is V*sin(55), and he travels a distance V*sin(55)*t.  Twin A is of course farther downstream than Twin B, but it doesn't affect their horizontal crossing.



so the ratio of their speeds corresponds to the ratio of their times:
feel free to send me a message if something isn't clear. and please rate me.
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