A horizontal cylindrical pipe consists of two coaxial sections, the section to the left has radius r1 and that to the right has radius r2. Inside the pipe, there is a piston in each section trapping an incompressible fluid of density ρ filled in the complete space between them. Constant pressures p1 and p2 (p1>p2) are maintained outside the pistons in the sections to the left and to the right respectively. When both the pistons acquire constant speeds towards the right, find their speeds.