4.4: Misc. separation of variables on wave equation problems
1. Consider the wave equation u_tt = c^2u_xx for vibrations in a tightly stretched string of length L with initial conditions u(x,0) = f(x) and u_t(x,0) = g(x) and different boundary conditions listed below. For each boundary condition listed below, solve the wave equation (provide coefficient formulas as well). Also in each case, what is lim_t->inf u(x,t)? (If this limit does not exist, write DNE. If this limit is infinite, write infinite).
(a) u(0,t) = u(L,t) = 0 (We did this one in the lecture video, so you may omit it from your homework submission. It is good practice, though.)
(b) u_x(0,t) = u_x(L,t) = 0. Hint: be careful to consider the h-ODE in the special case lambda = 0. Also, under what condition on g(x) does the displacement remain bounded, i.e. finite?
(c) u_x(0,t) = u(L,t) = 0
(d) u(0,t) = u_x(L,t) = 0