# Machine Design Questions and Answers – Power Screws Numericals

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

1. Find the torque required to raise the load of 15kN and mean diameter of triple threaded screw being 46mm. Also given pitch=8mm and coefficient of friction is 0.15.
a) 11831.06N-mm
b) 11813.06N-mm
c) 12811.06N-mm
d) None of the listed

Explanation: tanἀ=l/πd or ἀ=9.429’ as l=3p. tan Ǿ=0.15 or Ǿ=8.531’. M=W x d x tan (Ǿ+ἀ)/2.

2. What is the collar friction torque if outer and inner diameters are 100mm and 65mm respectively. Coefficient of friction is 0.15 and the load acting is of 15kN. Consider uniform wear theory.
a) 89886.6N-mm
b) 38796.5N-mm
c) 92812.5N-mm
d) 87645.5N-mm

Explanation: M=0.15 x W(D+d)/4.

3. For a double threaded screw, what will be the tangent of helix angle if nominal diameter and pitch are 100mm and 12mm respectively?
a) 0.045
b) 0.081
c) 0.094
d) 0.023

Explanation: tan ἀ= l/πd where l=2p, d=D-0.5p.

4. If for a trapezoidal thread, angle of thread is 15’ then what will be the replacement of the coefficient of friction which is 0.15.
a) 0.1553
b) 0.1335
c) 0.1667
d) 0.1776

Explanation: f=0.15 x sec 15’.

5. What will be efficiency of the screw in case of raising the load when coefficient of friction is 0.1553 and tangent of helix angle is 0.0813?
a) 34%
b) 45%
c) 54%
d) 43%

Explanation: Efficiency= tanἀ(1-0.1553 x tan ἀ)/(0.1553+tanἀ).
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6. A machine vice whose length of the handle is 150mm and the coefficient of friction for thread and collar are 0.15 and 0.17 respectively has a force applied at handle of 125N. Also the outer and inner diameters of collar are 55mm and 45mm respectively. Find the screw torque in terms of clamping force W if nominal diameter=22mm and pitch=5mm.
a) 3.567W N-mm
b) 2.286W N-mm
c) 3.564W N-mm
d) None of the mentioned

Explanation: M₁=Wd x tan(Ǿ+ἀ)/2 or M₁=W x (22-0.5×2.5)x tan(4.66’+8.531’)/2 as tan(ἀ)=l/πd and tanǾ=0.15.

7. A machine vice whose length of the handle is 150mm and the coefficient of friction for thread and collar are 0.15 and 0.17 respectively has a force applied at handle of 125N. Also the outer and inner diameters of collar are 55mm and 45mm respectively. Find the collar torque in terms of clamping force W assuming uniform wear theory if nominal diameter=22mm and pitch=5mm.
a) 4.5W
b) 5.4W
c) 4.25W
d) 3.37W

Explanation: M₂=0.17 x W x (55+45)/4 or M₂=4.25W N-mm.

8. A machine vice whose length of the handle is 150mm and the coefficient of friction for thread and collar are 0.15 and 0.17 respectively has a force applied at handle of 125N. Also the outer and inner diameters of collar are 55mm and 45mm respectively. Find the clamping force W if nominal diameter=22mm and pitch=5mm.
a) 4539.45N
b) 2868.73N
c) 3657.56N
d) 2134.34N

Explanation: Net torque=M₁+M₂ or 125 x 150=2.286W + 4.25W or W=2868.73N.

9. A machine vice whose length of the handle is 150mm and the coefficient of friction for thread and collar are 0.15 and 0.17 respectively has a force applied at handle of 125N. Also the outer and inner diameters of collar are 55mm and 45mm respectively. Find the overall efficiency if nominal diameter=22mm and pitch=5mm.
a) 18.12%
b) 12.18%
c) 21.23%
d) 23.21%

Explanation: Efficiency= W l/2π(M₁+M₂) where
M₁=2.286W [M₁=Wd x tan (Ǿ+ἀ)/2 or M₁=W x (22-0.5×2.5) x tan (4.66’+8.531’)/2 as tan(ἀ)=l/πd and tan Ǿ=0.15].
M₂=4.25W [M₂=0.17 x W x (55+45)/4 or M₂=4.25W N-mm],
l=5mm,
W=2868.73N [Net torque=M₁+M₂ or 125 x 150=2.286W + 4.25W or W=2868.73N].

10. Find the bending stress to which a screw of nominal diameter 22mm is subjected when the clamp exerts a force of 5kN acts on it. The screw is double threaded and pitch of screw is 5mm.Given: Coefficient of friction is 0.15.It is assumed operator exerts a force of 250N at the handle of length 275mm.
a) 123.45N/mm²
b) 132.54N/mm²
c) 142.54N/mm²
d) 124.45N/mm²

Explanation: Bending stress=32M/πdᵌ where M=250 x 275N-mm,d=22-2 x 0.5 x 5mm.

11. Find the torsional shear stress to which a screw of nominal diameter 22mm is subjected when the clamp exerts a force of 5kN on it. The screw is double threaded and pitch of screw is 5mm.Given: Coefficient of friction is 0.15.
a) 25.45N/mm²
b) 21.29N/mm²
c) 31.21N/mm²
d) 35.65N/mm²

Explanation: =16M/πd₂ᵌ where M=Wd₁ tan (Ǿ+ἀ)/2 where d₁=22-0.5 x 5,W=5000N,
tanἀ=2 x 5/[πx19.5] and d₂=19.5-0.5 x 5.

12. If bending stress in a screw is of magnitude 95N/mm² and torsional shear stress of magnitude 15N/mm², then what is the principal shear stress?
a) 48.7N/mm²
b) 54.3 N/mm²
c) 51.4 N/mm²
d) 49.8 N/mm²

Explanation: τ(max)=√(95/2)²+15².

13. The nominal diameter of the screw is 22mm and the allowable bearing pressure for the nut is 15N//mm². Find the length of the nut if pitch of the screw is
a) 15mm
b) 20mm
c) 25mm
d) 30mm

Explanation: z=4W/π S(d₁²-d₂²) where S=15N/mm²,d₁=22mm and d₂=17mm. Hencez=2.2 or z=3. Length of nut=zp or l=3 x 5= 15mm.

14. A but joint can be defined as a joint between two components lying approximately in a different plane.
a) True
b) False

Explanation: Butt joint is defined a joint between two plates lying in the same plane.

15. A fillet weld is an approximately triangular cross section joining two surfaces lying parallels to each other.
a) True
b) False

Explanation: Two surfaces lie perpendicular to each other.

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