[QUE/TH-03003] TH-PROBLEM

Calculate the work done when a van der Waals gas of volume $V_1$ expands to a volume $2V_1$ under (a) Constant temperature (b) Under constant pressure. The equation of the gas is
$$ \left(p\,+\,\frac{an^2}{V^2}\right)\left(V\,-\,nb\right)\,=\,nRT $$
where the symbols have the usual meanings. $a$ and $b$ are constants/