Exercise 2 solution

Open ocean, d = 4,000 m:
speed = square root of (9.8 x 4,000) = square root of 39,200 = about 198 m/s (about 713 km/h).

Travel time = 5,000 km / 713 km/h = about 7.0 hours. (Check: 5,000,000 m / 198 m/s = about 25,250 s = 7.0 h.)

Near the shore, d = 10 m:
speed = square root of (9.8 x 10) = square root of 98 = about 9.9 m/s (about 36 km/h).

The wave slows by a factor of about 20, so the wave front piles up: the water behind it catches up and the height increases sharply.