Theory of Machine
The Ackerman steering gear mechanism is preferred to the Davis steering gear mechanism, because

The Ackerman steering gear is most economical
The Ackerman steering gear consists of turning pairs
Both (A) and (B)
Whole of the mechanism in the Ackerman steering gear is on the back of the front wheels

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

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

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