4)- Consider a stretched string with mass per unit length u and tension "I". Disturbances obey the wave equation. At time t=0 the string is at rest but has a square wave disturbance of length "A" and height H centered on the origin. solve for the disturbance y(x,t) for t 0 when a) the string has length L and is clamped at rest at the boundaries + 1/2 b) the string is infinitely long. [Hint: Consider travelling waves for this b)]