The answer is: 5.665 seconds
Explanation:
Given:
Speed = v = 54 km/h
Change it to m/s; therefore,
Speed = v = 54 / 3.6 = 15 m/s
Wavelength = λ = 170 m
Since
v = fλ
So f = v/λ
Plug in the values:
f = 15/170 = 3/34 Hz
Now time = 1/frequency
=> t = 1/(3/34) = 34/3 = 11.33s
The time should be half as the trough to crust distance as λ/2; therefore
t = 11.33/2 = 5.665s