A dynamometer D is attached to two bodies of masses M = 6kg and m = 4 kg. Forces F = 20N and f = 10N are applied to the masses as shown. The dynamometer reads

Acceleration of system,                                     a=F-fM+m=20-106+4=1 ms-2 (towards left) Let F0 be the reading of dynamometer, then equation of motion of mass m would be              F0 - f = ma⇒  F0=f+ma=10+(4)(1)=14 N