Two motors in a factory are running at slightly different rates. One runs at 825.0 rpm and the other at 786.0 ${ rpm } .$ You hear the sound intensity increase and then decrease periodically due to wave interference. How long does it take between successive instances of the sound intensity increasing?
A) 1.54 s
B) 1.43 s
C) 1.66 s
D) 1.79 s

Question

Quizplus · Accepted Answer

The beat frequency is the difference in frequencies of the two motors: $ \frac{825.0 - 786.0}{60} = 0.65 $ Hz. The time between successive intensity increases is the inverse of the beat frequency: $ \frac{1}{0.65} \approx 1.54 $ s.

Two Motors in a Factory Are Running at Slightly Different rpm.{ rpm } .rpm.

Two Motors in a Factory Are Running at Slightly Different ${ rpm } .$