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| Math Central | Quandaries & Queries |
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Subject: uniform motion A motorboat can maintain a constant speed of 16 miles per hour relative to the water. The boat makes a trip upstream to a certain point in 20 minutes; the return trip takes 15 minutes. What is the speed of the current? |
Hello,
Use the fact that distance is velocity multiplied by time: d = v 
t.
The boat's velocity is going to be its velocity relative to the water, plus the velocity of the current.
d = (vboat + vcurrent) t
Let v be the velocity of the current downstream (you could pick upstream here, but I felt like picking downstream). Then the velocity of the current upstream (if we keep the boat's velocity at positive 16 miles per hour) is -v. The distance travelled going upstream is the same as the distance downstream.
From here can you set up an equation that lets you solve for v?
-Haley
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