Question

Please Help:

Answer 1

... The torpedo gets 20m farther away every second.
... After 100s, it's 2,000m away.

... It explodes.

... They hear it 101.4s after it was launched.
... That's 1.4s after the explosion.
... The sound covered the 2,000m back to them in 1.4 sec.

Speed = distance / time

= 2000m / 1.4s = 1,428.6 m/s (rounded)