[填空题]
A sailor strikes the tqbx l,98 muc/;aqp0j side o 0ltkqj(p mh/ (-ez4toqgrck 707 idf9f his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary signi0jm7qoig(f 4zt7qr- 9l (0 kedkthp/cficantly with depth. $ \times10^{ 3}$m
