Wave speed from period and wavelength

Steps:

• Identify period T from Graph 1 as time for one full cycle of displacement.
• Identify wavelength λ from Graph 2 as distance between two consecutive crests at fixed time.
• Use wave speed formula v = λ / T to compute numerical value.
• Plug in values: λ = 6.0 cm, T = 0.050 s, so v = 6.0 / 0.050 = 120 cm s^{-1}.

Why D is correct:

• Wave speed v equals wavelength λ divided by period T, yielding 120 cm s^{-1} from graph measurements.

Why the others are wrong:

• A: Underestimates speed by using twice the period (e.g., half-cycle time).
• B: Assumes incorrect λ of 4 cm or misreads T as 0.20 s.
• C: Overestimates by using λ / (T/3), ignoring full period.

Final answer: D