Wave speed from period and wavelength

Steps:

• Period T = 6.0 s (time between crests).
• Frequency f = 1/T = 1/6.0 ≈ 0.167 Hz.
• Wavelength λ = 2 × 4.5 m = 9.0 m (crest-to-trough is half wavelength).
• Speed v = f × λ = (1/6) × 9 = 1.5 m/s.

Why D is correct:

• Wave speed formula v = f λ, where f = 1/T and λ = twice crest-to-trough distance.

Why the others are wrong:

• A: Uses 4.5 m as full λ, giving v = (1/6) × 4.5 = 0.75 m/s, but ignores half-wavelength.
• B: Direct v = distance/T = 4.5/6 = 0.75 m/s, confusing distance with λ.
• C: Possible error like v = λ/T = 9/6 = 1.5 m/s but halved, or misapplied formula.

Final answer: D