Posted by Anne on Saturday, September 12, 2009 at 1:12pm.
Well, if he is going upstream, his boat velocity relative to water is 2.80cos45.
Watervelocity-boatveloicy=ground speed
so we need ground speed. WE know how far he went 120, but time. Well, easy. Going across the river, he went 280m with a velocity of 2.80sin45. So time in the water is 280/2.8sin45= 141 (check that) seconds
water velocity= ground speed+boatvelocity
water velocity= 120/141 m/s - 2.8*.707
and you can find it from that.
The negative means it is going opposite to the boat direction
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