1.

Two small balls A and B of positivecharge Q each and masses m and 2m respectively are connected by a non conducting light rod of length L. Thissystem is released in a uniform electric field of strength E as shown. Just after the release (assume no other force acts on the system)

Answer»

rod has zero angular ACCELERATION
rod has angular acceleration `(QE)/(2mL)` in anti-clockwise direction.
acceleration of point A is `(2QE)/(3m)` TOWARDS right
acceleration of point A is `(QE)/m` towards right.

Solution :Resultant force on arrangement is 2QE, thus acceleration of CENTRE of mass is given by
`a_C=(2QE)/(3m)` (towards right)
As per CONSERVATION of angular MOMENTUM
`QE((2L)/3)-QE(L/3)=[mxx(4L^2)/9+2mxxL^2/9]alpha`
`rArr alpha =(QE)/(2mL)` (clockwise)
From constrant equation, we get
`a_A=a_C+alpha ((2L)/3)`
`=(2QE)/(3m)+(QE)/(2mL)((2L)/3)`
`=(3QE)/(3m)=(QE)/m` (towards right)


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