y = A cos (wt) sin (kx)

y = A cos(2p /T)t sin(2p /T)x

at t = 0.28T and x = 0.04l

y = Acos[(2p /T)0.28T] sin[(2p /l )0.04l ] = 3.0 cos(0.28X2p ) sin(0.04X2p )

= 3.0cos100.8º sin14.4º = 3.0(-0.1784)(0.2487) = -0.14 mm
 

Note: The numbers 2760 and 195 given in the problem are irrelevant. If they are used in the solution they will just cancel out again.
 

Answer is E

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