Standard Spur Gears Questions & Answers :: Gear MCQ

1. Lewis equation for design of involute gear tooth predicts the dynamic load capacity of a cantilever beam of uniform strength.

a) True
b) False

Answer: b

Justification: Lewis equation for design of involute gear tooth predicts the static load capacity of a cantilever beam of uniform strength.

2. For a pair of gears in mesh, pressure angle and module must be different to satisfy the condition of interchangeability and correct gearing.

a) True
b) False

Answer: b

Justification: For a pair of gears in mesh, pressure angle and module must be same to satisfy the condition of interchangeability and correct gearing.

3. In skew bevel gears, the axes are
a) non-parallel and non-intersecting, and teeth are curved
b) non-parallel and non-intersecting, and teeth are straight
c) intersecting, and teeth are curved and oblique
d) intersecting, and teeth are curved and can be ground

Answer: a

Justification: Skew bevel gears imply non-parallel, non-intersecting and curved them.

4. In case the number of teeth on two bevel gears in mesh is 30 and 60 respectively, then the pitch cone angle of the gear will be
a) tan-12
b) п/2 + tan-12
c) п/2 – tan-10.5
d) tan-10.5

Answer: d

Justification: tanɸ = NP/NG

NP = No. of teeth of pinion
NG = No. of teeth of gear
ɸ = Pitch cone angle
ɸ = tan-1(30/60)
ɸ = tan-10.5.

5. Consider the following statements: The axes of spiral bevel gear are non-parallel and intersecting.

1. The most common pressure angle for spiral bevel gear is 20o.
2. The most common spiral angle for spiral bevel gear is 35o.
3. Spiral bevel gears are generally interchangeable.
4. Spirals are noisy and recommended for low speeds of 10 m/s.

Which of the above statements are correct?
a) 1 and 4
b) 1 and 2
c) 2 and 3
d) 3 and 4

Answer: a

Justification: Commonly used pressure angle is 20o, spiral gear operation is noisy hence recommended for low speed operation.

6. Consider the following statements:
In case of helical gears, teeth are cut at an angle to the axis of rotation of the gears.
1. Helix angle introduces another ratio called axial contact ratio.
2. Transverse contact ratio is equal to axial contact ratio in helical gears.
3. Large transverse contact ratio does not allow multiple teeth to share the load.
4. Large axial contact ratio will cause larger axial force component.

Which of the above statements are correct?
a) 1 and 2
b) 2 and 3
c) 1 and 4
d) 3 and 4

Answer: c

Justification: Transverse contact ratio may not be equal to axial contact ratio. Larger contact ratio means sharing of multiple teeth.

7. A worm gear set is designed to have pressure angle of 300 which is equal to the helix angle. The efficiency of the worm gear set at an interface friction of 0.05 is
a) 87.9%
b) 77.9%
c) 67.9%
d) 57.9%

Answer: a

Justification: ȵ = tanλ(cosɸ – μtanλ)/cosɸtanλ + μ
tanλ = -μ + √1 + μ2
tanλ = -(0.05) + √1 + (0.05)2
tanλ = 0.9512

ȵ = 89.1%

So most suitable option is ‘a’.

8. The use of straight or curved external gear teeth in mesh with internal teeth in gear and spline couplings is specifically employed to accommodate
a) torsional misalignment
b) parallel misalignment
c) angular misalignment
d) substantial axial movements between shafts

Answer: c

Justification: Straight or curved external gear teeth are used to correct the angular misalignment.

9. A planetary gear train is a gear train having
a) a relative motion of axes and the axis of at least one of the gears also moves relative to the frame
b) no relative motion of axes and no relative motion of axes with respect to the frame
c) no relative motion of axes and the axis of at least one of the gears also moves relative to the frame
d) a relative motion of axes and none of the axes of gears has a relative motion with the frame

Answer: a

Justification: Planetary gear train ensures the relative motion of at least one axis w.r.t. the frame.

10. The load on a gear tooth is 50 kN. If the gear is transmitting a torque of 6000 Nm, the diameter of the gear is approximately
a) 0.5 m
b) 0.75 m
c) 1 m
d) 0.25 m

Answer: d

Justification: T = w cosɸ x d/2
6000 = 50000 x 0.94 x d/2
d = 0.25 m.

11. A spur gear of 40 teeth is machined in a gear hobbing machine using a double start hob cutter. The speed ratio between the hob and the blank is

a) 1:20
b) 1:40
c) 40:1
d) 20:1

Answer: d

Justification: When a spur gear of 40 teeth is machined in a gear hobbing machine using a double start hob cutter. The speed ratio between the hob and the blank is 20:1.

12. A helical gear has the active face width equal to b pitch p and helix angle α. What should be the minimum value of b in order that contact is maintained across the entire active face of the gear?

a) p cosα
b) p secα
c) p tanα
d) p cotα

Answer: d

Justification: The minimum value of b in order that contact is maintained across the entire active face of the gear is b > p/tanα. or b > p cotα.

13. Match the type of gears with their most appropriate description.

Type of gear Description

P. Helical 1. Axes non parallel and intersecting
Q. Spiral 2. Axes parallel and teeth are inclined to the axis
R. Hypoid 3. Axes parallel and teeth are parallel to the axis
S. Rack and pinion 4. Axes are perpendicular and intersecting,and teeth are inclined to the axis
5. Axes are perpendicular and used for large speed reduction
6. Axes parallel and one of the gears has infinite radius

a) P-2, Q- 4, R- 1, S- 6
b) P-1, Q- 4, R- 5, S- 6
c) P-2, Q- 6, R- 4, S- 2
d) P-6, Q- 3, R- 1, S- 5

Answer: a

Justification

Helical – Axes parallel and teeth are inclined to the axis
Spiral – Axes are perpendicular and intersecting,and teeth are inclined to the axis
Hypoid – Axes non parallel and intersecting
Rack and pinion – Axes parallel and one of the gears has infinite radius.

14. Tooth interference in an external in volute spur gear pair can be reduced by

a) Decreasing center distance between gear pair
b) Decreasing module
c) Decreasing pressure angle
d) Increasing number of gear teeth

Answer: d

Justification: There are several ways to avoid interfering:

i. Increase number of gear teeth
ii. Modified involutes
iii. Modified addendum
iv. Increased centre distance.

15. Interference in a pair of gears is avoided, if the addendum circles of both the gears intersect common tangent to the base circles within the points of tangency.

a) True
b) False
Answer: a

Justification: Interference in a pair of gears is avoided, if the addendum circles of both the gears intersect common tangent to the base circles within the points of tangency

16. Twenty degree full depth involute profiled 19-tooth pinion and 37-tooth gear are in mesh. If the module is 5 mm, the centre distance between the gear pair will be

a) 140 mm
b) 150 mm
c) 280 mm
d) 300 mm

Answer: a

Justification: Centre distance = D1 + D2/2 = mT1 + mT2/2 = 5(19 + 37)/2 = 140 mm.

17. If the drive efficiency is 80%, then torque required on the input shaft to create 1000 N output thrust is

a) 20 Nm
b) 25 Nm
c) 32 Nm
d) 50 Nm

Answer: b

Justification: Module m = 2,
D/T = 2
∴ D = 80 × 2 = 160 mm
2F = 1000, or F = 500 N
Let T1 be the torque applied by motor.
TT2 be the torque applied by gear.
∴ Power transmission = 80%

Now, T1ω1= 2T2 x ω2/0.8
T1 = 25 N-m.

18. If the pressure angle of the rack is 20°, then force acting along the line of action between the rack and the gear teeth is

a) 250 N
b) 342 N
c) 532 N
d) 600 N

Answer: c

Justification: Pcos φ = F
∴ Force acting along the line of action,
P = F/cos φ
= 500/cos20°
= 532 N.

19. Two mating spur gears have 40 and 120 teeth respectively. The pinion rotates at 1200 rpm and transmits a torque of 20 Nm. The torque transmitted by the gear is

a) 6.6 Nm
b) 20 Nm
c) 40 Nm
d) 60Nm

Answer: d

Justification: We know, N1/N2 = T1/T2
N1 = speed of pinion
N2 = speed of gear wheel
T1 = number of teeth of gear
T2 = number of teeth of pinion

1200/N2 = 120/40
N2 = 400 r.p.m.
Since power transmitted by both gear will be equal
T1ω1= T2 x ω2

torque transmitted by gear, = 60 N-m.

20. The velocity ratio between pinion and gear in a gear drive is 2.3, the module of teeth is 2.0 mm and sum of number of teeth on pinion and gear is 99. What is the centre distance between pinion and the gear?

a) 49.5 mm
b) 99 mm
c) 148.5 mm
d) 198 mm

Answer: b

Justification: Centre distance = D1 + D2/2 = mT1 + mT2/2
= m/2(T1 + T2)
= 2/2 x 99 = 99 mm.

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