# Elements of Machine Design-08

## Design of power screws

1   Which of the following does not form the important part of the screw jack?
(A)   Frame
(B)   Nut
(C)   Cup
(D)   Coupling

2   What type of friction in cup design is recommended for the set screw?
(A)   Sliding
(B)   Rolling
(C)   Static
(D)   None of the mentioned

3   If the torque required to lower the load is negative it is called
(A)   overhauling screw
(B)   self-locking screw
(C)   either A or B
(D)   none of the above

4   A power screw is only used to convert rotary motion into linear motion and not for transmitting power.
(A)   TRUE
(B)   FALSE

5   A power screw has no problem of wear as there is very less amount of friction associated.
(A)   TRUE
(B)   FALSE

6   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

7   Trapezoidal threads are better than square threads as there is radial pressure or side thrust on the nut.
(A)   TRUE
(B)   FALSE

(A)   TRUE
(B)   FALSE

9   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

10   Nominal diameter of the screw thread is the same as core diameter.
(A)   TRUE
(B)   FALSE

11   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

12   If the nominal diameter of screw thread = 50mm and pitch = 10mm then the mean diameter of the screw thread will be?
(A)   40 mm
(B)   45 mm
(C)   60 mm
(D)   55 mm

13   Power screws are used to convert rotary motion into translatory motion.
(A)   TRUE
(B)   FALSE

14   When screw threads are to be used in a situation where power is being transmitted in one direction only, then the screw threads suitable for this will be

15   The railway carriage couplings have

16   The acme threads are usually found on
(A)   spindles of bench vices
(B)   railway carriage couplings
(C)   feed mechanism of machine tools

17   The efficiency of a square threaded screw is maximum if the helix angle is equal to (where Ø = Angle of friction)
(A)   90deg-Ø
(B)   45deg-Ø
(C)   45 deg-Ø/2
(D)   45deg+Ø/2

18   A screw will be self-locking, if
(A)   friction angle is less than helix angle
(B)   friction angle is more than helix angle
(C)   friction angle is equal to the helix angle
(D)   the efficiency of the screw is 100%

19   A screw is said to be over hauling screw if the
(A)   friction angle is less than helix angle
(B)   friction angle is more than helix angle
(C)   friction angle is equal to the helix angle
(D)   the efficiency of the screw is 100%

20   When the screw in a mechanical screw jack rotates, the load kept on the top of it moves
(A)   axially upwards
(B)   axially downwards
(C)   axially upwards or downwards
(D)   none of these

21   Which of the following screw thread is used for power transmission in one direction only?

22   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)   Overhauling
(C)   self-locking
(D)   None of the mentioned

23   A screw is said to be over hauling if its efficiency is
(A)   Equal to 50%
(B)   More than 50%
(C)   Less than 50%
(D)   None of the above

24   A cup is provided in screw jack
(A)   To reduce the friction
(B)   To prevent rotation of load
(D)   To increase efficiency

25   Screw jacks are found wherever?
(A)   need to lift
(B)   position
(D)   all of the above

(A)   it has relatively slow speed
(B)   it has poor efficiency
(C)   both A and B
(D)   none of A and B

27   Which one is correct?
(A)   lead screw of lathe is used to obtain a precise motion
(B)   universal testing machine is used to load a specimen
(C)   vice is used to clamp a work piece
(D)   both A, B, C are correct