A group of swimmers is resting in the sun on an off-shore raft. They estimate that 2.5 m separates a trough and an adjacent crest of surface waves on the lake. They count 15 crests that pass by the raft in 15 s. How fast are the waves moving?
_____m/s
λ=2•2.5=5 m
s=14•5=70 m
v=s/t=70/15=4.67 m/s