Two blocks, with masses m and 3m, are attached to the ends of a string with negligible mass that passes over a pulley, as shown above. The pulley has negligible mass and friction and is altached to the ceiling by a brackel. The blocks are simultaneously released from rest. (a) Derive an equation for the speed v of the block of mass 3m after i falls a distance d in Jerms of m. and physical constants, as appropriate