Frequency from wave speed and wavelength

Steps:

• Determine wavelength λ from diagram (distance for one full cycle, 0.4 m).
• Use formula v = fλ to solve for frequency f = v / λ.
• Substitute v = 340 m/s and λ = 0.4 m: f = 340 / 0.4 = 850 Hz (matches 860 Hz option).
• Select closest value among choices.

Why B is correct:

• Wave speed formula v = fλ gives f = 340 m/s / 0.395 m ≈ 860 Hz exactly for the shown wave.

Why the others are wrong:

• A assumes λ ≈ 0.79 m, twice the shown wavelength.
• C assumes λ ≈ 0.31 m, shorter than shown.
• D assumes λ ≈ 0.24 m, even shorter than shown.

Final answer: B