Since V0(t 1-t2)/t2 emits a continuous sound wave (time is t 1), let the span (front and back length) of this sound wave be X 1 = δ T 1 * v0.

When the sinking submarine receives the echo front sound wave, it begins to count the back sound wave received by the submarine, and the time given to * * * is t2.

During t2, the submarine sank x3.

The sound wave behind the echo also reaches the submarine within t2, and takes x2=v0*t2.

Then x3 = x1-x2 = t1* VO-T2 * v0.

Because it takes t2 time for the submarine to sink X3.

So the sinking speed of the submarine is v0(t 1-t2)/t2.