Water waves slow in shallow water due to reduced depth

Steps:

• Wave speed in water depends on depth: v = √(g h), where h is water depth.
• As the wave enters shallow water, h decreases, so speed v decreases.
• Wave frequency f remains constant during propagation.
• Wavelength λ = v / f, so if v decreases and f is constant, λ decreases.

Why D is correct:

• Speed decreases per v = √(g h) as h reduces; wavelength decreases since λ = v / f with constant f.

Why the others are wrong:

• A: Speed decreases, not increases, in shallow water.
• B: Speed decreases, not increases.
• C: Wavelength decreases, not increases, with constant f.

Final answer: D