A river crossing - Math Central

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Question from tara, a student:

A river has a constant current of 4 kilometers per hour. At what angle
to a boat dock should a motorboat, capable of maintaining a constant
speed of 20 kilometers per hour, be headed on order to reach a point
directly opposite the dock? If the river is 1/2 kilometer wide, how long
with it take to cross?

Hi Tara.

Here is a drawing I made.

river

Can you think of a trig function that you can use to calculate the
value of ?

How can you calculate the effective crossing speed x?

Once you know x, can you use it to calculate the time it takes to
cross 1/2 km at that speed?

Stephen La Rocque.>

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