Theory of Machine
A system of masses rotating in different parallel planes is in dynamic balance if the

Resultant couple is equal to zero
Resultant force and resultant couple are both equal to zero
Resultant force is equal to zero
Resultant force is numerically equal to the resultant couple, but neither of them need necessarily be zero

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Theory of Machine
A rotor which is balanced statically but not dynamically is supported on two bearings L apart and at high speed of the rotor, reaction on the left bearing is R. The right side of the bearing is shifted to a new position 2L apart from the left bearing. At the same rotor speed, dynamic reaction on the left bearing in the new arrangement will

Become equal to R/4
Remain same as before
Become equal to 2R
Become equal to R/2

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