posted by Anne .
A boat, whose speed in still water is 2.80m/s , must cross a 280m wide river and arrive at a point 120m upstream from where it starts. To do so, the pilot must head the boat at a 45.0 degrees upstream angle. What is the speed of the river's current?
Well, if he is going upstream, his boat velocity relative to water is 2.80cos45.
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