Question

A double parallelogram mechanism is shown in the figure. Note that PQ is a single link. The mobility of the mechanism is

• A. -1
• B. 0
• C. 1
• D. 2

Answer 1

The correct option is C 1



In this case, one link is redundant i.e. function of mechanism is not affected even if any one of thinks, (2), (3) or (4) are removed.
So, the effective number of links.

$l=4,j=4\text{and}h=0$
$DOF=3(l-1)-2j-h$
$=3(4-1)-2\times 4-0$
$=1$