Three blocks with masses \(m , 2 m\) and \(3 m\) are connected by strings, as shown in the figur....

Three blocks with masses \(m , 2 m\) and \(3 m\) are connected by strings, as shown in the figure. After an upward force \(F\) is applied on block \(m\), the masses move upward at constant speed \(v\). What is the net force on the block of mass \(2 m\) ? ( \(g\) is the acceleration due to gravity)