A man holds an umbrella vertically up while walking due west with a constant velocity of 1.5 m/s to protect himself from the rain. He can
rotate the umbrella by an angle of 30 degree and still protect himself
from the rain when he stops walking. What is the velocity of the rain?

Afisherman notices that his boat is moving up and down periodically without any horizontal motion, owing to waves on the surface of the water. it takes a time of 2.20 s for the boat to travel from its highest point to its lowest, a total distance of 0.670 m . the fisherman sees that the wave crests are spaced a horizontal distance of 5.80 m apart. (a) how much is the wavelength? (b) find the period of the wave. (c) how fast are the waves traveling? (d) what is the amplitude a of each wave?