Posted by Anonymous on Tuesday, February 26, 2008 at 7:35pm.
There is not enough information, was there a previous question or other info?
The river flowed at 10 km/hr
the boat went at 24 km/hr
The boat must head upstream such that 24 sin T = 10
or T = 24.6 degrees upstream of straight across
By the way, his speed across the river is now 24 cos 24.6 degrees = 21.8 km/hr
By the way, this is why you swim aiming toward the other bank and let yourself be swept downstream. If you try to head enough upstream to make a path straight across to a selected spot on the other bank, you will take longer getting across assuming you do not mind landing downstream on the other bank.
In the limit, as the current reaches your swimming speed, you will never reach the other side, whereas if you just aim for the other bank and let the current take you as it wishes, at least you will get to the other side if somewhat downstream.
The answer says 65 degrees upstream. I don't know how they got that.
Well, I did 24.6, call it 25 degrees from straight across.
That is 90 - 25 = 65 degrees from the bank.
I think the question was designed by a mathematician, not a navigator :)
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