1. The problem statement, all variables and given/known data 2. Relevant equations Heat equation 3. The attempt at a solution I can derive E(t) to get integral of du/dt over 0 to L, which is the same as integrating the right hand side of the original equation (d2u/dx2+sin(5t); while this allows me to take care of the d2u/dx2, I don't know what to do with the sin(5t) term or proceed from there. Thanks.