# Power Screws - Mechanical Engineering (MCQ) questions and answers

1)   Calculate lead angle of a thread which has mean diameter of 45 mm and lead of 10 mm

a. 8.5o
b. 4.04o
c. 3.02o
d. None of the above
 Answer  Explanation ANSWER: 4.04o Explanation: No explanation is available for this question!

2)   Calculate overall efficiency of power screw, if the torque applied by the operator is 150 x 103 to move a load of 30 kN through a distance of 10 mm

a. 22.36 %
b. 37.69 %
c. 31.83 %
d. 30.23 %
 Answer  Explanation ANSWER: 31.83 % Explanation: No explanation is available for this question!

3)   Determine torque required to overcome collar friction in square threaded screw, if coefficient of friction is 0.12 and axial force of 20 kN is exerted by the screw. Mean radius of friction collar is 20 mm

a. 48000 N-mm
b. 120 N-mm
c. 4800 N-mm
d. 12000 N-mm
 Answer  Explanation ANSWER: 48000 N-mm Explanation: No explanation is available for this question!

4)   Which type of stress is induced in a screw thread ?

a. Torsional shear stress
c. Bearing pressure
d. All of the above
 Answer  Explanation ANSWER: Bearing pressure Explanation: No explanation is available for this question!

5)   A single start square threaded power screw supports  load of 30 kN which has outer diameter of 30 mm and a pitch of 8 mm. Maximum shear stress of 30 N/mm2 is induced in a screw body. Determine number of screw threads considering direct shear stress.

d. None of the above

6)   A triple start square threaded power screw has torsional shear stress and direct compressive stress of 5 N/mm2 and 7 N/mm2. Calculate maximum shear stress induced in a screw body.

a. 7.4 N/mm2
b. 3.5 N/mm2
c. 6.10 N/mm2
d. 5 N/mm2
 Answer  Explanation ANSWER: 6.10 N/mm2 Explanation: No explanation is available for this question!

7)   In power screws, if friction angle Φ is less than lead angle λ, then the screw undergoes _______

a. over hauling
b. self locking
c. both a. and b.
d. none of the above
 Answer  Explanation ANSWER: over hauling Explanation: No explanation is available for this question!

8)   The efficiency of power screw can be improved if ______

a. the rolling friction is replaced by sliding friction in the screw threads
b. the sliding friction is replaced by rolling friction in the screw threads
c. both a. and b.
d. none of the above
 Answer  Explanation ANSWER: the sliding friction is replaced by rolling friction in the screw threads Explanation: No explanation is available for this question!

9)   Calculate torque required to overcome thread friction if axial load of 8 kN acts on a power screw having double start square threads of 30 mm mean diameter. Friction angle and lead angle are 7o and 9o respectively

a. 68.81 N-m
b. 41.90 N-m
c. 34.40 N-m
d. Insufficient data
 Answer  Explanation ANSWER: 34.40 N-m Explanation: No explanation is available for this question!

10)   Which type of stress is induced in a screw body?

a. Bearing pressure
b. Direct shear stress
c. Torsional shear stress
d. None of the above
 Answer  Explanation ANSWER: Torsional shear stress Explanation: No explanation is available for this question!