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Statement I: In four-bar chain, whenever all four links are used, with each of them forming a turning pair, there will be continuous relative motion between the two links of different lengths. Statement II: For a four-bar mechanism, the sum of the shortest and longest link lengths is not greater than the sum of remaining two links.

Statement I: In four-bar chain, whenever all four links are used, with each of them forming a turning pair, there will be continuous relative motion between the two links of different lengths. Statement II: For a four-bar mechanism, the sum of the shortest and longest link lengths is not greater than the sum of remaining two links. Correct Answer Both Statement I and Statement II are individually true, and Statement II is the correct explanation of Statement I 

A kinematic chain with four binary inks and four revolute pairs is called a 4-bar kinematic chain. When any one link is fixed, it becomes a mechanism and is called a 4-bar linkage.

The shortest link is of length S and longest link is of length L the other two links are of lengths P and Q respectively.

In a 4-bar linkage continuous relative motion between any two is possible only if the sum of the lengths of the shortest and longest link is less than the sum of the lengths of the other two links. This is called Grashof's rule.

i.e. For continuous relative motion between two links

S + L < P + Q

If S + L > P + Q, no link can move continuously and we will get only rocker-rocker mechanism even if any link is fixed.

Therefore both the statements are true and statement II) is the correct explanation of statement I).

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