[填空题]
A sailor strikes the side of q v.ef9( .ksvih((fpx his shipbi 1ybf8cu;(ypac e:+vkl(db 6m /(d5 fa,wxp just below the waterline. He hears the echo of x,(d/5m kiu1 lpyebfd:;6p cafcbwbvy 8(a+(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 significantly with depth. $ \times10^{ 3}$m