Echo return time equals half the bang interval

Steps:

• Distance to cliff is 80m, so round-trip distance for echo is 160m.
• Bangs occur every 1 second.
• Echo heard halfway between bangs means it returns after 0.5 seconds.
• Speed of sound = total distance / time = 160m / 0.5s = 320 m/s.

Why D is correct:

• Matches formula v = d/t, where d=160m (round trip) and t=0.5s (half interval).

Why the others are wrong:

• A: Implies 160m in 4s, but echo returns in 0.5s.
• B: Implies 160m in 2s, exceeding 0.5s return time.
• C: Implies 160m in 1s, twice the actual 0.5s.

Final answer: D