Table 1 shows the depth of a lake, measured using ultrasound pulses, at various distances from a jetty.
| Distance from jetty (m) | Depth of the lake (m) |
|---|---|
| 0 | 0.0 |
| 20 | 3.2 |
| 40 | 6.5 |
| 60 | 8.0 |
| 80 | 10.5 |
| 100 | 13.0 |
| 120 | 15.5 |
| 140 | 18.0 |
| 160 | 19.5 |
A researcher on a survey boat uses ultrasound pulses to measure the depth of the lake when the boat is positioned exactly 140 m from the jetty.
Calculate the total round-trip time of travel for the ultrasound pulse key to this measurement.
The speed of the ultrasound pulse in the lake water is 1500 m/s.