MCQs on Efficiency of Screws
1 - Question
Efficiency of screw depends upon lead of the screw.
a) True
b) False
View Answer
Answer: a
Explanation: Efficiency= WL/[Pπd].
2 - Question
Efficiency of the screw depends upon helix angle but does not depend on friction angle.
a) True
b) False
View Answer
Answer: b
Explanation: Efficiency=tan(ἀ)/tan(Ǿ+ἀ) where ἀ=Helix angle and Ǿ=Friction angle.
3 - Question
Efficiency of the screw _______ with increase of coefficient of friction.
a) decreases
b) increases
c) has no effect
d) cannot be determined
View Answer
Answer: a
Explanation: Efficiency is inversely proportional to tan of the sum of helix and efficiency angle.
4 - Question
Maximum efficiency of a square threaded is given by
a) 1-sinǾ/1+sinǾ
b) 1+sinǾ/1-sinǾ
c) 1-2sinǾ/1+2sinǾ
d) 1+2sinǾ/1-2sinǾ
View Answer
Answer:
Explanation: Efficiency=Sin(2ἀ+Ǿ)-Sin Ǿ /Sin(2 ἀ+Ǿ+Sin Ǿ),For max efficiency, sin(2ἀ+ Ǿ)=1
5 - Question
If friction angle is 30’ then the maximum efficiency of the screw is
a) 33%
b) 66%
c) 50%
d) Noe of the mentioned
View Answer
Answer: a
Explanation: Maximum efficiency=1-sinǾ/1+sinǾ.
6 - Question
Maximum possible efficiency of a self-locking screw is
a) 50%
b) 75%
c) 66%
d) 33%
View Answer
Answer: a
Explanation: For self locking screw Ǿ(friction angle)>ἀ (helix angle), hence efficiency < tanǾ/tan(Ǿ+ἀ) or efficiency < tanǾ(1-tan²Ǿ)/2tanǾ.
7 - Question
In trapezoidal threads, f (coefficient of friction) can be taken as
a) f sec θ
b) f cos θ
c) f sin θ
d) f cosec θ
View Answer
Answer: a
Explanation: The normal force acting on the thread is W sec θ therefore the effect of the thread angle is to increase the frictional force by a term sec θ.
8 - Question
Clutch and coupling can be considered to be same.
a) True
b) False
View Answer
Answer: b
Explanation: Clutch is a temporary join while coupling is a permanent joint.
9 - Question
Cold rolled components have higher strengths and hardness than hot rolled components.
a) True
b) False
View Answer
Answer: a
Explanation: During grain re-structuring, original strength of material is lost.
10 - Question
Which of the following are true?
a) Cold working reduces toughness and ductility
b) Cold worked components have poor resistance to shocks and vibrations
c) Tooling for cold working is cheaper as compared to hot working
d) All of the mentioned
View Answer
Answer: d
Explanation: Properties of cold working.