# Machine Design Questions and Answers – Power Screws & Self Locking Screws

This set of Machine Design Multiple Choice Questions & Answers (MCQs) focuses on “Power Screws & Self Locking Screws-Basics”.

1. A power screw is only used to convert rotary motion into linear motion and not for transmitting power.
a) True
b) False

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

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

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

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

Explanation: Trapezoidal and not square threads suffer from the problem of bursting.

a) True
b) False

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

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
c) Diameter
d) None of the mentioned

9. Nominal diameter of the screw thread is the same as core diameter.
a) True
b) False

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

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

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

Explanation: Self locking takes place if load does not descend on its own and that is possible only in c condition.

Sanfoundry Global Education & Learning Series – Machine Design.
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