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# Machine Kinematics MCQ – Standard Spur Gears-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

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Answer: b

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

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

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Answer: b

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

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

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Answer: a

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

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^{-1}2

b) п/2 + tan^{-1}2

c) п/2 – tan^{-1}0.5

d) tan^{-1}0.5

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Answer: d

Explanation: tanɸ = N_{P}/N_{G}

N_{P} = No. of teeth of pinion

N_{G} = No. of teeth of gear

ɸ = Pitch cone angle

ɸ = tan^{-1}(30/60)

ɸ = tan^{-1}0.5.

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 20^{o}.

2. The most common spiral angle for spiral bevel gear is 35^{o}.

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

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Answer: a

Explanation: Commonly used pressure angle is 20^{o}, spiral gear operation is noisy hence recommended for low speed operation.

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

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Answer: c

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

A worm gear set is designed to have pressure angle of 30^{0} 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%

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Answer: a

Explanation: ȵ = tanλ(cosɸ – μtanλ)/cosɸtanλ + μ

tanλ = -μ + √1 + μ^{2}

tanλ = -(0.05) + √1 + (0.05)^{2}

tanλ = 0.9512

ȵ = 89.1%

So most suitable option is ‘a’.

The use of straight or curved external gear teeth in mesh with internal teeth in gear and spline couplings is specifically employed accommodate

a) torsional misalignment

b) parallel misalignment

c) angular misalignment

d) substantial axial movements between shafts

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Answer: c

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

A planetary gear train is 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 relative motion with the frame

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Answer: a

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

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

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Answer: d

Explanation: T = w cosɸ x d/2

6000 = 50000 x 0.94 x d/2

d = 0.25 m.