1. Efficiency of the screw _______ with increase of coefficient of friction.
a) decreases
b) increases
c) has no effect
d) cannot be determined
Explanation: Efficiency is inversely proportional to tan of the sum of helix and efficiency angle.
2. 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
Explanation: Efficiency=Sin(2ἀ+Ǿ)-Sin Ǿ/Sin(2 ἀ+Ǿ+Sin Ǿ),For max efficiency, sin(2ἀ+ Ǿ)=1.
3. If friction angle is 30’ then the maximum efficiency of the screw is
a) 33%
b) 66%
c) 50%
d) Noe of the mentioned
Explanation: Maximum efficiency=1-sinǾ/1+sinǾ.
4. Maximum possible efficiency of a self-locking screw is
a) 50%
b) 75%
c) 66%
d) 33%
Explanation: For self locking screw Ǿ(friction angle)>ἀ (helix angle), hence efficiency < tanǾ/tan(Ǿ+ἀ) or efficiency < tanǾ(1-tan²Ǿ)/2tanǾ.
5. 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
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.
6. Clutch and coupling can be considered to be same.
a) True
b) False
Explanation: Clutch is a temporary join while coupling is a permanent joint.
7. Cold rolled components have higher strengths and hardness than hot rolled components.
a) True
b) False
Explanation: During grain re-structuring, original strength of material is lost.
8. 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
Explanation: Properties of cold working.
9. Threaded joints are non-separable joints.
a) True
b) False
Explanation: Threaded joints are separable joints of machine parts that are held together by means of a threaded fastening such as nut and bolt.
10. Which type of joints is better when the product is subjected to large vibrations: welded or threaded?
a) Welded
b) Threaded
c) Both have same results
d) Depends on the magnitude of the vibrational force
Explanation: Threaded joints loosen when subjected to vibrations.