A sound wave has frequency of 2 kHz and wavelength of 35 cm. If an observer is 1.4 km away from the source, after what time interval could the observer hear the sound?

- 0.5 s
- 2 s
- 4 s
- 20 s

**Answer**

Speed of wave = Wavelength x Frequency

d/t = 0.35 m x 2000 Hz = 700 m/s

Time = Distance / Speed = 1400/700 = 2 s

**The correct option is B.**