Question

Linked Answer Questions:
A quick return mechanism is shown below. The crank OS is driven at 2 rev/s in counter clockwise direction.


If the quick return ratio is 1: 2, then the length of the crank in mm is

• A. 250
• B. 250$\sqrt{3}$
• C. 500
• D. 500$\sqrt{3}$

Answer 1

The correct option is A 250

Given:
$\frac{2\theta }{2\pi -2\theta }=\frac{1}{2}$



$\therefore \theta =\frac{\pi }{3}$
In triangle OMP

$cos\theta =\frac{r}{OP}$,

$cos\left(\frac{\pi }{3}\right)=\frac{r}{500}$

or $r=250$ mm

Point to Remember

While solving these types of questions, students should keep in mind that quick-return ratio is (> 1) or (< 1) and then according to the given data, take the ratio of forward and return stroke.