Answer :
By using the concept of Interference, surface displacement of the water wave is 4cm
We know that when two waves interfere with each other ,they will be two possibility either they will interfere in same phase and other one is when they interfere in opposite phase
Here the two waves interfere with each other in same phase so the new wave which produces after superimposition with each other, amplitude add up and produce a new amplitude with sum of amplitude of given two waves
Therefore surface displacement of the water wave when the crest of one wave meets a crest of the other wave =(2+2)cm =4cm
Hence, surface displacement of water wave is 4cm
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