Trevor can row a boat at 3.00 mi/hr in still water. He needs to cross a river that is 1.20 miles wide with a current flowing at 1.60 mi/h. Not having his calculator ready, he guesses to go straight across, he should head 60.0 degrees upstream with respect to straight across. a) what is his speed with respect to the starting point on the shore? b) how long does it take to cross the river? c) what should the angle have been to have gone directly across the river?

Question

roadjester · Answer

"... he guesses to go straight across, he should head 60.0 degrees upstream with respect to straight across. "

This line is a bit confusing to me. So he SHOULD to at a 60 degree angle but instead goes straight across at 0.0 degrees?

anonymous · Answer

i have no idea, i'm confused to with that part..
i got the answer of a, but i still dont get it why the solution is like this O.o
|dw:1392580215528:dw|
if it's like this, how will i get letter c???

roadjester · Answer

wait, so he's going WITH the current? not against it?

anonymous · Answer

oh, it should be like this, sorry
|dw:1392580639374:dw|

roadjester · Answer

ok, you're working with vectors. Since part (a) asked you what his speed going straight across was, it doesn't affect his motion in the direction of the river. the X and Y components are independent of each other.

anonymous · Answer

yes.........

roadjester · Answer

ok, i thick i got something but...

roadjester · Answer

think*

anonymous · Answer

aah get what you mean
but the problem says 3 mi/hr is the speed of the boat "in still water" 
so don't you think 3 mi/ h will be the vertical like this: |dw:1392581264648:dw|