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Material Type: Assignment; Professor: Tenali; Class: Intro to Linear Algebra; Subject: Mathematics; University: Florida Institute of Technology; Term: Spring 2009;
Typology: Assignments
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Practice Problems - Wave Equation
MTH3102 Spring 2009
(1) Determine the solution of the following initial value problems: (a) utt − c^2 uxx = 0, u(x, 0) = sin x ut(x, 0) = x^2. (b) utt − c^2 uxx = 0, u(x, 0) = cos x ut(x, 0) = x. (2) Determine the solution of the initial- boundary value problem: utt − 16 uxx = 0 , 0 < x < ∞, t > 0 u(x, 0) = sin x, 0 < x < ∞ ut(x, 0) = x^2 , 0 < x < ∞ u(0, t) = 0 , t > 0 (3) Determine the solution of the initial- boundary value problem: utt − 9 uxx = 0 , 0 < x < ∞, t > 0 u(x, 0) = 0 , 0 < x < ∞ ut(x, 0) = x^3 , 0 < x < ∞ ux(0, t) = 0 , t > 0 (4) Solve the following initial boundary value problem by method of seperation of variables: utt − c^2 uxx = 0 , 0 < x < π, t > 0 u(x, 0) = 3 sin x, 0 < x < π ut(x, 0) = 0 , 0 < x < π u(0, t) = u(π, t) = 0. (5) Solve the following initial boundary value problem by method of seperation of variables: utt − c^2 uxx = 0 , 0 < x < π, t > 0 u(x, 0) = 0 , 0 < x < π ut(x, 0) = 8 sin^2 x, 0 < x < π u(0, t) = u(π, t) = 0. (6) Solve the following initial boundary value problem by method of seperation of variables: utt − c^2 uxx = 0 , 0 < x < π, t > 0 u(x, 0) = sin x, 0 < x < π ut(x, 0) = x^2 − πx, 0 < x < π u(0, t) = u(π, t) = 0. (7) Solve the following initial boundary value problem by method of seperation of variables: utt − c^2 uxx = 0 , 0 < x < π, t > 0 u(x, 0) = cos x, 0 < x < π ut(x, 0) = 0 , 0 < x < π ux(0, t) = ux(π, t) = 0. 1
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(8) A string is streched between the fixed points 0, and 1 on the x axis, and released at rest from the position y = A sin πx, where A is a constant. Obtain an expression for the subsequent displacements y(x, t). (9) A string streched between the points 0 and π on the x axis and initially at rest, is released from position y = f (x).Its motion is opposed by resistence, which is proportional to the velocity at each point. Let the unit of time chosen so that the equation of motion becomes ytt = yxx − 2 βyt, 0 < x < π, t > 0 where β is a positive constant. Assuming, 0 < β < 1 derive the expression
y(x, t) = e−βt
n=
Bn
cos αnt +
β αn
sin αnt
sin nx
where αn =
n^2 − β^2 , Bn = (^2) π
∫ (^) π 0 f^ (x) sin^ nx dx, n^ = 1,^2 ,^ · · ·^. (10) The ends of a streched string are fixed at the origin and at the point x = π on the horizontal x axis. The string is initially at rest along the x axis and then drops under its own weight. The vertical displacements y(x, t) satisfies the DE ytt = a^2 yxx − g, 0 < x < π, t > 0 where g is accelaration due to gravity. Use the method of variation of paramaters to find the dispalcements.