# Machine Kinematics Questions and Answers – Length Of Arc of Contact

This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Length Of Arc of Contact”.

1. If the centre distance between a pair of spur gears in mesh is 240 mm and the pinion moves five times faster than the gear, then the pitch circle diameters of pinion and gear respectively are
a) 40mm and 200 mm
b) 80mm and 400 mm
c) 60mm and 300 mm
d) 50mm and 250 mm
View Answer

Answer: b
Explanation: rp + rg = 240
rp/rg = 5
rg = 200 mm, dg = 400 mm
rp = 40 mm, dp = 80 mm.

2. Pressure angle of involute gears does not exceed 250, since
a) this will lead to unwanted radial force
b) the number of teeth to avoid undercutting will be very high
c) no cutters are available
d) gear will become too small
View Answer

Answer: a
Explanation: Pressure angle of involute gears does not exceed 250, since Gear is curved.

3. Worm and worm wheel drive can be reversible.
a) True
b) False
View Answer

Answer: a
Explanation: If friction angle > lead angle we cannot determine whether drive is reversible or not.
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4. Two involute gears are designed to mesh for a given centre distance and a given angular velocity ratio (other than 1). During assembly, the centre distance has increased slightly. Then which of the following changes occur?
(i) Velocity ratio changes
(ii) Pressure angle changes
(iii) Pitch circle diameter changes
(iv) Working depth changes
(v) Base circle radius changes
Select the correct answer using the code given below.
a) 1, 2 and 3
b) 2, 3 and 4
c) 2 and 5
d) 3 and 5
View Answer

Answer: b
Explanation: When Centre to centre distance increases then pressure angle, depth, pitch circle diameter changes. Velocity ratio and base circle radius will remain same.

5. Which of the following statements are correct for mating gears with involute profiles?
(i) The pressure angle, from the start of the engagement to the end of the engagement, remains constant.
(ii) The pressure angle is maximum at the beginning of the engagement, reduces to zero at pitch point, starts decreasing and again becomes maximum at the end of the engagement.
(iii) The face and flank of the teeth are generated by a single curve and the normal to this curve at any point is tangent to the base circle of the gear.
(iv) The centre distance for a pair of mating gears can be varied within limits without altering the velocity ratio.
Select the correct answer using the code given below.
a) 1, 3 and 4
b) 1 and 3 only
c) 2 and 4 only
d) 2,3 and 4
View Answer

Answer: a
Explanation: The pressure angle varies only for cycloidal gears.
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6. The velocity ratio in the case of the compound train of wheels is equal to
a) No. of teeth on first driver/No.of teeth on last follower
b) No. of teeth on last follower/No.of teeth on first driver
c) Product of teeth on the drivers/Product of teeth on the followers
d) Product of teeth on the followers/Product of teeth on the drivers
View Answer

Answer: c
Explanation: In compound trains, velocity ratio = Product of teeth on the drivers/Product of teeth on the followers.

7. Match list I with list II
List I List II
A. Compound train 1. Hart mechanism
B. Quick return mechanism 2. Coriolis force
C. Exact straight line motion 3. Transmission of motion around bends and corners
D. Approximate straight line motion 4. Watt mechanism

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a) A-1,B-2,C-3,D-4
b) A-3,B-2,C-1,D-4
c) A-3,B-4,C-1,D-2
d) A-1,B-4,C-3,D-2
View Answer

Answer: b
Explanation: Compound train – Transmission of motion around bends and corners
Quick return mechanism – Coriolis force
Exact straight line motion – Hart mechanism
Approximate straight line motion – Watt mechanism.

8. Consider the following statements:
When two gears are meshing, the clearance is given by the
1. difference between dedendum of one gear and addendum of the mating gear.
2. difference between total and the working depth of a gear tooth.
3. distance between the bottom land of one gear and the top land of the mating gear.
4. difference between the radii of the base circle and the dedendum circle.

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Which of these statements are correct?
a) 1,2 and 3
b) 2,3 and 4
c) 1,3 and 4
d) 1,2 and 4
View Answer

Answer: d
Explanation: the clearance can be found by following points 1,2 and 4.

9. In a simple gear train, if the number of idler gears is odd, then the direction of motion of driven gear will
a) be same as that of the driving gear
b) be opposite to that of the driving gear
c) depend upon the number of teeth on the driving gear
d) depend upon the total number of teeth on all gears of the train
View Answer

Answer: a
Explanation: In case of odd number of gears in a simple gear train, then the direction of motion of driven gear will be same as that of driving gear.

10. An epicyclic gear train has 3 shafts A,B and C. A is an input shaft running at 100 r.p.m. clockwise. B is an output shaft running at 250 r.p.m. clockwise. Torque on a is 50 kNm. C is a fixed shaft. The torque to fix C
a) is 20 kNm anticlockwise
b) is 30 kNm anticlockwise
c) is 30 kNm clockwise
d) cannot be determined as the data is insufficient
View Answer

Answer: a
Explanation: TA ωA = TB ωB
50 x 100 = TB x 250
or, TB = 20 kNm
Torque on C will be same as on B but in inverse direction.

Sanfoundry Global Education & Learning Series – Machine Kinematics.
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