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# Machine Kinematics Questions and Answers – Velocity in Mechanisms – 1

In the figure given below A and D are fixed points, link AB rotates at a uniform angular velocity of 900 rev/min ccw, find the instantaneous velocity of point E in m/s.

Rab = 100mm, Bc = 450, distance of E from BC = 100mm, Cf = 75mm, CD = 275mm, AD = 250mm, perpendicular DF = 17mm, perpendicular BE = 250mm.

a) 8.3

b) 8.7

c) 9

d) 7.6

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Answer: a

Explanation: The following question can be solved graphically as well as analytically,

first we find that

Vb = ωxRab = 9.42 m/s

Vcb = 11.42

Vcd = 13.61 m/s

constructing a velocity graph, we find that

Ve = 8.3m/s.

Velocity of a point B in a link can be calculated by using the relation

Vb = Va – Vba.

a) True

b) False

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Answer: b

Explanation: The velocity of a point B in a link can be calculated when the velocity of point A is known using the relation

Vb = Va + Vba.

In the figure given below A and D are fixed points, link AB rotates at a uniform angular velocity of 900 rev/min ccw, find instantaneous velocity of point F in m/s.

Rab = 100mm, Bc = 450, distance of E from BC = 100mm, Cf= 75mm, CD = 275mm, AD =250mm, perpendicular DF = 17mm, perpendicular BE = 250mm.

a) 8.3

b) 8.7

c) 9.4

d) 7.6

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Answer: c

Explanation: The following question can be solved graphically as well as analytically,

first we find that

Vb = ωxRab = 9.42 m/s

Vcb = 11.42

Vcd = 13.61 m/s

constructing a velocity graph, we find that

Vf = 9.4 m/s.

In the figure given below A and D are fixed points, link AB rotates at a uniform angular velocity of 900 rev/min ccw, find angular velocity of BC in rad/s.

Rab = 100mm, Bc = 450, distance of E from BC = 100mm, Cf= 75mm, CD = 275mm, AD =250mm, perpendicular DF = 17mm, perpendicular BE = 250mm.

a) 28.3

b) 2 8.7

c) 29.4

d) 25.3

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Answer: d

Explanation: The following question can be solved graphically as well as analytically,

first we find that

Vb = ωxRab = 9.42 m/s

Vcb = 11.42

ωcb = Vcb/Rcb

= 25.37 rad/s.

In the figure given below A and D are fixed points, link AB rotates at a uniform angular velocity of 900 rev/min ccw, find angular velocity of CDin rad/s.

Rab = 100mm, Bc = 450, distance of E from BC = 100mm, Cf= 75mm, CD = 275mm, AD =250mm, perpendicular DF = 17mm, perpendicular BE = 250mm.

a) 48.37

b) 48.77

c) 49.47

d) 45.37

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Answer: c

Explanation: The following question can be solved graphically as well as analytically,

first we find that

Vb = ωxRab = 9.42 m/s

Vcd = 13.61 m/s

ωcd = Vcd/Rcd

= 49.47 rad/s.

The locus of the instantaneous centre in space during a definite motion of the body is called the _________

a) Space centrode

b) Body centrode

c) Link centrode

d) Mechanism centrode

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Answer: a

Explanation: The instantaneous centre is a point inside the body which may be considered fixed at any instant of time. The locus of the instantaneous centre in space during a definite motion of the body is called the space centrode.

The locus of the instantaneous centre relative to the body itself is called the _________

a) Space centrode

b) Body centrode

c) Link centrode

d) Mechanism centrode

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Answer: b

Explanation: The instantaneous centre is a point inside the body which may be considered fixed at any instant of time. The locus of the instantaneous centre relative to the body itself is called the body centrode.

Locus of all instantaneous centres is known as centrode.

a) True

b) False

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Answer: a

Explanation: Thus the instantaneous centre of a moving body can be defined as that centre which goes on changing from one instant to another. The locus of all such instantaneous centres is known as a centrode.

A line drawn through an instantaneous centre and perpendicular to the plane of motion is called __________

a) Instantaneous axis

b) Relative axis

c) Instantaneous centrode

d) Relative centrode

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Answer: a

Explanation: A line drawn through an instantaneous centre and perpendicular to the plane of motion is called instantaneous axis. The locus of this axis is known as axode.

The locus of which axis is known as axode?

a) Instantaneous axis

b) Relative axis

c) Instantaneous centrode

d) Relative centrode

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Answer: a

Explanation: A line drawn through an instantaneous centre of the links and perpendicular to the plane of motion is known as instantaneous axis. The locus of this axis is known as axode.