A thin uniform rod of mass m moves translationally with acceleration a due to two antiparallel force of lever arm I. One force is of magnitude F and acts at one extreme end. The length of the rod is:
Let L be the length of the rod and F1 the magnitude of other force C is the center of the rod.
F1−F=ma
F1=F+ma....(i)
Now, net torque about center of the rod should be zero
F(L2)=F1(L2−I)
now, put the value of F1 from equation (i)
F(L2)=F+ma(L2−I)
F(L2)=F+ma(L2)−(F+ma)I
F(L2)=F(L2)+ma(L2)−(F+ma)I
L=2(F+ma)Ima
Hence, the length of the rod is 2(F+ma)Ima