Calculating Wave Speed: Pier Fishing Observation

[JJones_86]

Homework Statement

A person fishing from a pier observes that four crests pass by in 7.35 s and estimates the distance between two successive crests as 7 m. The timing starts with first crest and ends with fourth crest. What is the speed of the wave?

Homework Equations

f = 1/T
v = f*d

The Attempt at a Solution

T = 7.35s/4 = 1.8375
F = 1/T = 1/1.8375 = .544218
V = .544218 * 7m = 3.81

Can someone tell me what I'm doing wrong? Thanks!

 

[RoryP]

try using v=λ*f

 

[JJones_86]

Thats what i did...
V = .544218 * 7m

isnt λ = .544218?

 

[RoryP]

oh right, well i got v=2.86 m/s

 

[ak1948]

The problem states the timing starts with the first and ends with the fourth wave.

 

[RoryP]

yeah precisely. you have to read the question carefully.