# Theory of Machines – Section 1

21. When the two elements of a pair have a surface contact when relative motion takes place and the surface of one element slides over the surface of the other, the pair formed is known as a

A. lower pair
B. higher pair
C. self-closed pair
D. force-closed pair

22. The center distance between two meshing involute gears is equal to 23. The two elements of a pair are said to form a __________ when they permit relative motion between them.

A. open pair
B. kinematic pair

24. When the axes of the shafts, over which the gears are mounted, move relative to a fixed axis, then the train is known as a reverted gear train.

A. Right
B. Wrong

25. In under damped vibrating system, the amplitude of vibration

A. decreases linearly with time
B. increases linearly with time
C. decreases exponentially with time
D. increases exponentially with time

Correct Answer: C. decreases exponentially with time

26. The dynamic friction is the friction experienced by a body when the body

A. is in motion
B. is at rest
C. just begins to slide over the surface of the other body
D. none of the above

Correct Answer: A. is in motion

27. The steering of a ship means

A. movement of a complete ship up and down in vertical plane about transverse axis
B. turning of a complete ship in a curve towards right or left, while it moves forward
C. rolling of a complete ship side-ways
D. none of the above

Correct Answer: B. turning of a complete ship in a curve towards right or left, while it moves forward

28. The tractive force in a locomotive with two cylinders is given by (where c = Fraction of reciprocating parts per cylinder, m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, and θ = Angle of inclination of crank to the line of stroke)

A. m2.r cos θ
B. c.m2.r sin θ
C. (1 – c)m2.r(cos θ – sin θ)
D. m2.r(cos θ – sin θ)

Correct Answer: C. (1 – c)m2.r(cos θ – sin θ)

29. The radial distance of a tooth from the pitch circle to the bottom of the tooth is called

A. dedendum