# Identify the current expression for Kutzbach's criterion of mobility, given n is the number of links, j1 is the number of low-pair joints and j2 is th

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Identify the current expression for Kutzbach's criterion of mobility, given n is the number of links, j1 is the number of low-pair joints and j2 is the number of high-pair joints.
1. m = 2 (n - 1) - j1 - j2
2. m = 3 (n - 1) - j1 - 2j2
3. m = 3 (n - 1) - 2j1 - j2
4. m = 3 (n - 1) + j1 - j2

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Correct Answer - Option 3 : m = 3 (n - 1) - 2j1 - j2

Explanation:

Degree of freedom(DOF)/Mobility of linkage –

• Degree of freedom of plane mechanism is defined as the number of inputs or independent coordinates needed to define the configuration or
• position of all the links of mechanism with respect to a fixed link.

Kutzback equation of degree of freedom,

F = 3 × (n – 1) – 2j1 – j2

Where, n = number of links in the mechanism, j1 = Binary joint or lower pair, j2 = higher Pair and F = Degree of freedom

Grubler's criterial applies to planar mechanism having no higher pairs (h = 0) and completely constraint (F = 1).

1 = 3 × (n – 1) – 2j

∴ 1 = 3n – 3 –  2j

∴ 2j  – 3n + 4 = 0