Adistance of 1.0 × 10^−2 meter separates successive
crests of a periodic wave produced in a shallow
tank of water. if a crest passes a point in the tank
every 4.0 × 10^−1 second, what is the speed of this
wave?
(1) 2.5 × 10^−4 m/s (3) 2.5 × 10^−2 m/s
(2) 4.0 × 10^−3 m/s (4) 4.0 × 10^−1 m/s

There are 2 formulae you will need to use in this question, v=f*lambda where f is the frequency and lambda is the wavelength. The second one is f=1/T where f is the frequency and T is the time.

Firstly, let's work out f:

f=1/(4*10^-1)=2.5Hz

Then, we can substitute it into the second equation to work out the speed:

v=2.5*(1*10^-2)=0.025= 2.5*10^-2 m/s