A stationary sonar buoy sends a pulse into seawater

PHYSICS · Single correct · A Level · Physics · Waves · Waves

Problem

A stationary sonar buoy sends a

1500\,\text{Hz}

pulse into seawater, where the speed of sound is

1500\,\text{m}\!\cdot\!\text{s}^{-1}

. The pulse reflects from a submarine moving directly toward the buoy, and the buoy detects the returning echo at

1575\,\text{Hz}

. What is the submarine’s speed and direction? (a)

37\,\text{m}\!\cdot\!\text{s}^{-1}

away from the buoy (b)

75\,\text{m}\!\cdot\!\text{s}^{-1}

toward the buoy (c)

37\,\text{m}\!\cdot\!\text{s}^{-1}

toward the buoy (d)

26\,\text{m}\!\cdot\!\text{s}^{-1}

toward the buoy