Posted by Anonymous on .
How do I draw the following problem so I have something to refer to when answering a) and b)?
A river is 2 km wide and flows at 6 km/h. A motor boat that has a speed of
20 km/h in still water heads out from one bank perpendicular to the current.
A marina lies directly across the river on the opposite bank.
a. How far downstream from the marina will the boat reach the other bank? (0.6 km)
b. How long will it take? (6 min)

Math 
drwls,
Although the boat is pointed directly across, it does not travel perpendicular to shore. This is because, relative to the land, there is a Vx = 6 km/h component along the stream direction due to the river flow. There is also a Vy component of 20 km/h across the stream. The crossing time is 2.0 km/20 km/h = 0.1 h (6 minutes). The distance the boat drifts downstream in that time is 6 km/h*0.1h = 0.6 km