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NihalSh
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Homework Statement
The displacement due to a wave moving in the positive x-direction is given by ##y=\frac{1}{1+x^2}## at time t=0 s and by ##y=\frac{1}{1+(x-1)^2}## at t=2 s, where x and y are in meters. Find the velocity of the wave in m/s.
Homework Equations
## \frac{∂^2y}{(∂x)^2}=\frac{1}{v^2}.\frac{∂^2y}{(∂t)^2}##
The Attempt at a Solution
Since we have to deal with partial derivative wrt x on L.H.S., we can simply take the derivative of given x-y relations.
For case, t=0 we have:
##y=\frac{1}{1+x^2}##
or ##y.(1+x^2)=1##
differentiating on both sides wrt x, we get
##(1+x^2).\frac{∂y}{∂x}=-2.x.y##
differentiating again and substituting value of y, we get
## \frac{∂^2y}{(∂x)^2}=\frac{2.(3.x^2-1)}{(1+x^2)^3}##
Similarly for case t=2, we get:
## \frac{∂^2y}{(∂x)^2}=\frac{2.(3.(x-1)^2-1)}{(1+(x-1)^2)^3}##
The only common factor they seem to have is 2 so that must be equal to ##\frac{1}{v^2}##.
##\frac{1}{v^2}=2##
that means ##v= \sqrt{\frac{1}{2}} m/s≈0.71 m/s##
But my book says the answer is ##v=0.5 m/s##, I haven't got a clue what went wrong or how to approach it with some other method.
Any help would be greatly appreciated, thanks.
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