The canoeist crossing a river

  • Thread starter r.meghdies
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  • #1
r.meghdies
A canoeist who can paddle 5km/h in still water wishes to cross a 400 m wide river, with 2km/h current. If he steers the canoe perpendicular to the current and wants to get straight across the river how long will it take him to cross the river.

Which way is right? and why?

hypotenuse = 5 km/h
................| (ignore dots)
................| < 2 km/h
__________|
^ 400 m & 4.58 km/h
Θ = 22*

option 1:

t = 0.4 km / 4.58 km/h


option 2:
cosΘ = a / h
cos 22 = 0.4 km / h
h = 0.43 km

now i do t= .43km / 4.58 km/h

t= 5.63 minutes
 
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