Mechanical Engineering >> TOM-I

Question 1 : Define Machine

Answer : Machine is a device which utilise the available energy into some useful work. It consists of various parts in which one may be fixed and other parts move relative to that fixed part.
It must has basic three features to perform any work.
1. Mechanism- which makes the machine into working condition.
2. The point of application of effort.
3. The point where load is lifted or work is done.
Machines are classified as:
a. Simple Machine.
b. Compound Machine.

Question 2 : Define Structure

Answer : Structure:-
It is define as collection or assemblage of resistance bodies having no relative motion between them.
1. Unlike machine it is not used for transforming the available energy into some useful work.
2. Members of structure transfers load or force only.

Question 3 : Difference between Machine and Structure. (PTU, Dec. 06)

Answer : The Difference between Machine and Structure is as shown below:-

Question 4 : Define Kinematic Link.

Answer : Part of a machine which moves relative to some other part of machine is called kinematic link.
or
Parts of a machine which have no relative motion between them and behave like a single body of a machine and move relative to some other part of machine is called kinematic link.
It may be classified as:-
1. Rigid Link
2. Flexible Link
3. Fluid Link
As shown in fig. 4.1.

Question 5 : Define Kinematic Pair. Classify it on various account.

Answer : When the relative motion between two links of machine is in a definite direction then the pair is called “Kinematic Pair”.
In this the motion may be successfully or completely constrained.
Classification of kinematics pair :-

Question 6 : Explain Completely Constrained motion (PTU, Dec. 05)

Answer : When motion between pair is independent of direction of applied force and limited to a definite direction only, then motion is called completely constrained motion.
For examples:-
1. Motion of Square bar in a square hole as shown in fig. 5.1 below. In this bar can only slides inside the hole and the other motion like rotation is not possible.

2. Motion of shaft in a circular hole with collars at each ends in a hole as shown in fig. 5.2. In this shaft can only rotates inside the hole and other motion like sliding is not possible.

Question 7 : Explain Incompletely Constrained motion.

Answer : When motion between the pairs is depends upon the direction of force applied and it can take place according to direction of applied force then motion is called incompletely constrained motion.
In this, motion can take place in more than one direction. For examples:-
Motion of circular shaft in a circular hole as shown in fig 7.1, as it may be rotate or slide according to direction of applied force. In this both motions (sliding and rotary) are independent to each other.

Question 8 : Explain Successfully Constrained motion.

Answer : When motion between the pairs is not completed by itself but by some other means, then motion is called Successfully Constrained motion.
For examples:-
1. Motion of engine valves which are operated by rocker arms.
2. Reciprocating motion of piston inside the cylinder.
3.Block the axial upward movement of shaft in a “ Foot Step Bearing” by applied axial load on the shaft so that it can rotate in a bearing only.

Question 9 : Differentiate the completely constrained motion and successfully constrained motion. (PTU, May 2009)

Answer : Difference between the completely constrained motion and successfully constrained motion. are as shown below.

Question 10 : Define Sliding Pair. Give examples.

Answer : When two elements of a pair are connected in such a manner that one can only slide relative to the other then pair is called Sliding pair.
For examples:-
1. Motion of piston in engine cylinder, as in this piston can only slide inside the cylinder.

2. Motion of rectangular rod in rectangular hole.

As motion in sliding pair is depends upon the direction of applied force so it has completely constrained motion.

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