Math 127 trigonometry

Question

To approximate the speed of a stream's current, a paddle wheel with a radius of 6 feet is lowered into the water. 

If the stream causes the wheel to rotate at 11 rpm, what is the speed of stream in miles per hour? (1 mile= 5280 feet)

Round your answer to 2 decimal places

___ mph

Answer 1

A point on the circumference of the paddle wheel travels the same linear speed as the water in the stream.

Use dimensional analysis:

11 revs / 1 min · 12π ft / 1 rev ⋅ 1 mile / 5,280 ft · 60 mins / 1 hr = 1.5π mph ~ 4.71 mph