Homework Help: Trig

Posted by GoMeGo on Sunday, May 22, 2011 at 1:05am.

A boat heads S 15 degrees E on a river that flows due west. the boat travels S 11 degrees W with a speed of 25 km per hour. Find the speed of the current and the speed of the still water.

This is due tomorrow.

Trig - Reiny, Sunday, May 22, 2011 at 8:43am
Draw a vector AB , S15°E, showing the boat in still water.
Draw BC, going West, showing the speed of the river.
Join AC , the resultant vector.
By simple calculation of angles,
angle A = 26°
angle B = 75°
angle C = 79°

I see two simple applications of the sine law

for the speed of the river:
a/sin26° = 25/sin75°
a = 25sin26/sin75 = 11.35

for the boat's speed in still water:
c/ain79 = 25/sin75
c = 25.406

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