Paper 3, Section I, D

Complex Methods
Part IB, 2013

Let y(t)=0y(t)=0 for t<0t<0, and let limt0+y(t)=y0\lim _{t \rightarrow 0^{+}} y(t)=y_{0}.

(i) Find the Laplace transforms of H(t)H(t) and tH(t)t H(t), where H(t)H(t) is the Heaviside step function.

(ii) Given that the Laplace transform of y(t)y(t) is y^(s)\widehat{y}(s), find expressions for the Laplace transforms of y˙(t)\dot{y}(t) and y(t1)y(t-1).

(iii) Use Laplace transforms to solve the equation

y˙(t)y(t1)=H(t)(t1)H(t1)\dot{y}(t)-y(t-1)=H(t)-(t-1) H(t-1)

in the case y0=0y_{0}=0.