# Machine Kinematics Questions and Answers – Spur Gears

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This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Spur Gears”.

1. The gears are termed as medium velocity gears, if their peripheral velocity is
a) 1–3 m / s
b) 3–15 m / s
c) 15–30 m / s
d) 30–50 m / s

Explanation: The gears having velocity less than 3 m/s are termed as low velocity gears and gears having velocity between 3 and 15 m / s are known as medium velocity gears. If the velocity of gears is more than 15 m / s, then these are called high speed gears.

2. The size of gear is usually specified by
a) pressure angle
b) pitch circle diameter
c) circular pitch
d) diametral pitch

Explanation: It is the diameter of the pitch circle. The size of the gear is usually specified by the pitch circle diameter. It is also called as pitch diameter.

3. A spur gear with pitch circle diameter D has number of teeth T. The module m is defined as
a) m = d / T
b) m = T / D
c) m = π D / T
d) m = D.T

Explanation: Module is the ratio of the pitch circle diameter in millimetres to the number of teeth. It is usually denoted by m. Mathematically,
Module, m = D / T.
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4. In a rack and pinion arrangement, the rack has teeth of _______________ shape.
a) square
b) trepazoidal
c) oval
d) circular

Explanation: None.

5. The radial distance from the _______________ to the clearance circle is called working depth.
b) dedendum circle
c) pitch circle
d) none of the mentioned

Explanation: Working depth is radial distance from the addendum circle to the clearance circle. It is equal to the sum of the addendum of the two meshing gears.

6. The product of the diametral pitch and circular pitch is equal to
a) 1
b) 1/π
c) π
d) π × No. of teeth

Explanation: Diametral pitch, pd =T/D = π/pc
Circular pitch, pc = πD/T
Therefore, pd x pc = π.

7. The backlash for spur gears depends upon
a) module
b) pitch line velocity
c) tooth profile
d) both (a) and (b)

Explanation: Backlash is the difference between the tooth space and the tooth thickness, as measured on the pitch circle.

8. The contact ratio for gears is
a) zero
b) less than one
c) greater than one
d) none of the mentioned

Explanation: The ratio of the length of arc of contact to the circular pitch is known as contact ratio i.e. number of pairs of teeth in contact.

9. If the centre distance of the mating gears having involute teeth is increased, then the pressure angle
a) increases
b) decreases
c) remains unchanged
d) none of the mentioned

Explanation: The pressure angle increases with the increase in centre distance.

10. The form factor of a spur gear tooth depends upon
a) circular pitch only
b) pressure angle only
c) number of teeth and circular pitch
d) number of teeth and the system of teeth

Explanation: Form factor is independent of the size of the tooth and depends only on the number of teeth on a gear and the system of teeth.

11. Lewis equation in spur gears is used to find the
a) tensile stress in bending
b) shear stress
c) compressive stress in bending
d) fatigue stress

Explanation: None.

12. The minimum number of teeth on the pinion in order to avoid interference for 20° stub system is
a) 12
b) 14
c) 18
d) 32

Explanation: None.

13. The allowable static stress for steel gears is approximately ____________ of the ultimate tensile stress.
a) one-fourth
b) one-third
c) one-half
d) double

Explanation: The allowable static stress (σo) for steel gears is approximately one-third of the ultimate tensile strength
u) i.e. σo = σu / 3.

14. Lewis equation in spur gears is applied
a) only to the pinion
b) only to the gear
c) to stronger of the pinion or gear
d) to weaker of the pinion or gear

Explanation: The Lewis equation is applied only to the weaker of the two wheels (i.e. pinion or gear).

a) less than
b) greater than
c) equal to
d) none of the mentioned