Machine Design MCQ:
1. A power screw is only used to convert rotary motion into linear motion and not for transmitting power.
A. True
B. False
.
Answer: B
Explanation: Power screw converts the motion from rotary to linear and is used for power transmission.
2. Depending upon the holding arrangement, power screws operate in how many different arrangements.
A. 2
B. 3
C. 4
D. 5
.
Answer: A
Explanation: There are two types of arrangements. In one screw rotates while nut remains stationary and vice versa.
3. A power screw has no problem of wear as there is very less amount of friction associated.
A. True
B. False
.
Answer: B
Explanation: Wear is a serious problem in power screws as there is high friction in threads.
4. V threads are highly recommended for fastening as well as power transmission purpose.
A. Yes
B. Never
C. In some cases
D. Can’t be stated
.
Answer: B
Explanation: In fastening, high frictional force is required and hence V threads are used whereas in power transmission, reduction in frictional forces is required.
5. Trapezoidal threads are better than square threads as there is radial pressure or side thrust on the nut.
A. True
B. False
.
Answer: B
Explanation: Trapezoidal and not square threads suffer from the problem of bursting.
6. Trapezoidal threads screws have less load carrying capacity as compared to square thread screws.
A. True
B. False
.
Answer: B
Explanation: Square threads have less thickness at the core diameter and hence lower load carrying capacity.
7. Which of the following are true for buttress threads?
A. Combination of square and trapezoidal threads
B. Transmit motion in one direction only
C. They are used in vices
D. All of the mentioned
.
Answer: D
Explanation: As force is applied only in one direction in a vice so buttress threads are used.
8. Tr 40 x 14(P 7), here 14 indicates
A. Pitch
B. Lead
C. Diameter
D. None of the mentioned
.
Answer: B
Explanation: Tr=Trapezoidal threads,14=Lead(mm),7=Pitch(mm).
9. Nominal diameter of the screw thread is the same as core diameter.
A. True
B. False
.
Answer: B
Explanation: Nominal diameter is the largest diameter while core diameter is the smallest diameter of the screw thread.
10. If nominal diameter of screw thread=50mm and pitch=10mm then the mean diameter of the screw thread will be?
A. 40mm
B. 45mm
C. 60mm
D. 55mm
.
Answer: B
Explanation: Diameter(mean)=Diameter(nominal) – 0.5P .
11. If the load itself begin to the screw and descend down, unless a restraining torque is applied then the condition is termed as
A. Halting
B. Overhaulting
C. Front driving
D. None of the mentioned
.
Answer: B
Explanation: Overhaulting is the condition when load itsel begin to turn the screw.
12. Self-locking takes place when
A. Coefficient of friction is equal to or greater than the tangent of the helix angle
B. Coefficient of friction is lesser than or equal to the tangent of the helix angle
C. Coefficient of friction is equal to or greater than the tangent of the helix angle
D. None of the mentioned
.
Answer: C
Explanation: Self locking takes place if load does not descend on its own and that is possible only in c condition.
13. Efficiency of screw depends upon lead of the screw.
A. True
B. False
.
Answer: A
Explanation: Efficiency= WL/[Pπd].
14. Efficiency of the screw depends upon helix angle but does not depend on friction angle.
A. True
B. False
.
Answer: B
Explanation: Efficiency=tan(ἀ)/tan(Ǿ+ἀ) where ἀ=Helix angle and Ǿ=Friction angle.
15. Efficiency of the screw _______ with increase of coefficient of friction.
A. decreases
B. increases
C. has no effect
D. cannot be determined
.
Answer: A
Explanation: Efficiency is inversely proportional to tan of the sum of helix and efficiency angle.
16. 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
.
Answer: A
Explanation: Efficiency=Sin(2ἀ+Ǿ)-Sin Ǿ/Sin(2 ἀ+Ǿ+Sin Ǿ),For max efficiency, sin(2ἀ+ Ǿ)=1.
17. If friction angle is 30’ then the maximum efficiency of the screw is
A. 33%
B. 66%
C. 50%
D. Noe of the mentioned
.
Answer: A
Explanation: Maximum efficiency=1-sinǾ/1+sinǾ.
18. Maximum possible efficiency of a self-locking screw is
A. 50%
B. 75%
C. 66%
D. 33%
.
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.
19. 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
.
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.
20. Clutch and coupling can be considered to be same.
A. True
B. False
.
Answer: B
Explanation: Clutch is a temporary join while coupling is a permanent joint.
21. Cold rolled components have higher strengths and hardness than hot rolled components.
A. True
B. False
.
Answer: A
Explanation: During grain re-structuring, original strength of material is lost.
22. 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
.
Answer: D
Explanation: Properties of cold working.
