Math CentralQuandaries & Queries


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.


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

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.>

About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS