# Theory of Machines Questions and Answers – Quick Return Mechanisms

This set of Theory of Machines Multiple Choice Questions & Answers (MCQs) focuses on “Quick Return Mechanisms”.

1. For what purpose are the quick return mechanisms used?
a) To convert reciprocating motion into oscillatory motion
b) To convert oscillatory motion into reciprocating motion
c) To convert reciprocating motion into rotary motion
d) To convert rotary motion into reciprocating motion

Explanation: Due to the rotation motion of the disc, the ram moves forward and backwards. During half rotation, the ram moves forward whereas during the other half rotation. The ram quickly returns. Thus it converts rotary motion into reciprocating motion.

2. In a quick return mechanism, the forward reciprocating motion is faster rate than the backward stroke. True or false?
a) True
b) False

Explanation: In a quick return mechanism, the forward reciprocating motion is slower rate as compared to the backward stroke. That is why it is called a quick return mechanism.
Thus, the statement is false.

3. For a crank and slotted lever quick return mechanism, α = 150°. Find the ratio of time of cutting stroke to time of return stroke.
a) 1.2
b) 1.3
c) 1.4
d) 1.5

Explanation: Ratio of the time of cutting stroke to the time of return stroke for a crank and slotted lever quick return mechanism = (360-α)/α = (360-150)/150 = 1.4.

4. For a crank and slotted lever quick return mechanism,β = 260°. Find the ratio of time of cutting stroke to time of quick return stroke.
a) 2.6
b) 1.6
c) 0.2
d) 0.4

Explanation: : Ratio of time of cutting stroke to time of return stroke for a crank and slotted lever quick return mechanism = β/(360-β) = 260/(360-260) = 2.6.

5. For a Whitworth quick return motion mechanism α = 200°. Find the ratio of time of cutting stroke to time of return stroke.
a) 1.25
b) 1.35
c) 1.30
d) 1.40

Explanation: : Ratio of time of cutting stroke to time of return stroke for a Whitworth quick return motion mechanism= α/(360-α) = 200/(360-200) = 1.25.

6. For a Whitworth quick return motion mechanism β = 110°. Find the ratio of time of cutting stroke to time of return stroke.
a) 0.44
b) 2.27
c) 2.37
d) 0.42

Explanation: Ratio of time of cutting stroke to time of return stroke for a Whitworth quick return motion mechanism = (360-β)/ β = (360-110)/110 = 2.27.

7. A crank and slotted lever quick return mechanism has a centre distance of 1000 mm between the centre of oscillation of slotted lever and centre of rotation of the crank. Radius of the crank is 420 mm. Find the ratio of time of cutting stroke to time of return stroke. a) 1.677
b) 6.901
c) 6.248
d) 1.762

Explanation: AC = 1000 mm and BC = 420 mm
sin(90-α/2) = BC/AC = 0.42
90- α/2 = 24.834
α = 130.33°
Ratio of time of cutting stroke to time of return stroke = (360-α)/α = (360-130.33)/130.33
= 1.762.

8. In a crank and slotted lever quick return mechanism, the distance between the fixed centres is 400 mm and the length of the crank is 250 mm. If the length of the slotted bar is 2000 mm, find the length of the stroke if the line of stroke passes through the extreme positions of the free side of the lever. a) 1500 mm
b) 2000 mm
c) 1000 mm
d) 2500 mm

Explanation: AC = 400 mm, CB = 250 mm and AB = 2000 mm
sin(90- α/2) = BC/AC = 0.625
α = 102.63°
Length of stroke = 2 x AB sin(38.68°) = 2500 mm.

9. In a Whitworth quick return mechanism, distance between the fixed centres is 30mm and the length of the driving crank is 60 mm. The length of the slotted lever is 100 mm and the length of the connecting rod is 85 mm. Find the ratio of time of cutting stroke to time of return stroke. a) 1.5
b) 2.5
c) 2
d) 1

Explanation: CD = 30 mm, CA = 60 mm, PA = 100 mm, PR = 85 mm
cos β/2 = 0.5
β = 120°
Ratio of time of cutting stroke to time of return stroke = (360-β)/ β = (360-120)/120 = 2.

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