A stationary motion detector sends sound waves of 0.225 MHz toward a truck approaching at a speed of 33.0 m/s. The speed of sound in the air is 343 m/s. What is the frequency of the waves reflected back to the detector

0.273 MHz

Explanation:

The frequency f₁ of the reflected waves to the stationary detector is given by

f₁ = f (v + v₁) / (v - v₂) where f = frequency of sound waves = 0.225 MHz, v = speed of sound in air = 343 m/s, v₁ = speed of detector = speed of truck = 33.0 m/s and v₂ = speed of source of reflected wave = speed of truck = 33.0 m/s

f₁ = f (v + v₁) / (v - v₂)

= 0.225MHz (343 m/s + 33 m/s) / (343 m/s - 33 m/s)

= 0.225MHz * 376/310

= 0.273 MHz