A research ship uses sonar to measure the depth of the seabed. The speed of the sonar pulse in water is 1500 m/s. The seabed is 3000 m below the ship. A sonar pulse is emitted from the ship. How long is it before the sonar pulse returns to the ship? Use the equation: distance travelled=speed×time\text{distance travelled} = \text{speed} \times \text{time}distance travelled=speed×time.
1.0 s1.0\text{ s}1.0 s
2.0 s2.0\text{ s}2.0 s
4.0 s4.0\text{ s}4.0 s
8.0 s8.0\text{ s}8.0 s