Wednesday, 23 November 2011

QUESTION BANK : ENGINEERING MECHANICS PART-2

TOPICS: NUMERICALS ON FORCE SYSTEM- UNIT-1


5) A bar of AB 12 m long rests in horizontal position on two smooth planes as shown in the figure. Find the distance X at which 100 kN is to be placed to keep the bar in equilibrium.



 
6) A light string ABCDE whose extremity A is fixed, has weights W1 & W2 attached to it at B & C. It passes round a small smooth pulley at D carrying a weight of 300 N at the free end E as shown in figure. If in the equilibrium position, BC is horizontal and AB & CD make 150° and 120° with BC, find (i) Tensions in the strings and (ii) magnitudes of W1 & W2  


 
7) Find reactions at all the contact points if weight of P is 200 N & diameter is 100 mm, where as weight of Q is 500 N and diameter is 180 mm.









 
8) Determine the force P required to begin rolling the uniform cylinder of mass (m) over the obstacle of height (h) as shown in the figure.  







 
9) A roller of weight 500 N has a radius of 120 mm and is pulled over a step of height 60 mm by a horizontal force P. Find magnitudes of P to just start the roller over the step.




 
10) Two identical rollers each of weight 100 N are supported by an inclined plane of 30° with horizontal and a vertical wall as shown in the figure. Find all the reactions at each contact point.






 
11) A smooth cylinder of radius 500 mm rests on a horizontal plane and is kept from rolling by a rope OA of 1000 mm length. A bar AB of length 1500 mm and weight 1000 N is hinged at point A and placed against the cylinder of negligible weight. Determine the tension in the rope.






 

12)      A flat belt connects pulley B, which drives a pulley A; attached to an electric motor. μs =  0.25 and μk = 0.2 between both the pulleys and the belt. If maximum allowable tension in the belt is 600 N, determine the largest torque which can be exerted by belt on pulley B.




      

13)       Two blocks of mass MA & MB are kept at equilibrium as shown in the figure. The friction between the block B & the floor is 0.35 and between the blocks is 0.3, then find the minimum force P to just move the block B.

Monday, 14 November 2011

QUESTION BANK : ENGINEERING MECHANICS


Compiled by Er. Subhankar Karmakar
Unit: 1 (Force System)

VERY SHORT QUESTIONS (2 marks):

1)      What is force & force system?
2)      What is equilibrium? What are the conditions of equilibrium?
3)      Distinguish between coplanar concurrent & coplanar non-concurrent forces.
4)      State & explain the law of transmissibility of forces.
5)      What is moment? What is couple?
6)      State and explain the Varignon’s theorem of moment.
7)      What are the characteristics of couple?
8)      What are parallel forces?
9)      State Lami’s theorem of equilibrium of forces?
10)  Where do we can apply Lami’s theorem?
11)  Explain the terms Resultant & equilibrant?
12)  What is friction? On what factors frictional force depends?
13)  Explain the term Ladder Friction?
14)  What is angle of friction, angle of repose, co-efficient of friction?
15)  Explain the concept of Limiting friction.
16)  Explain the cone of friction. Also discuss it’s physical significance?
17)  State Coulomb’s law of dry friction?
18)  What is a belt drive? Explain the term angle of contact or lap angle.
19)  Explain the term Torque, Couple and Moment?
20)  Distinguish between static and dynamic friction.

BROAD QUESTIONS (5 marks / 10 marks)

1)      Classify Force systems with proper examples.
2)      State & prove Lami’s theorem.
3)      State & prove Varignon’s theorem of moment.
4)      What is the resultant of a force system? How can we determine the resultant?
5)      What are support reactions? Describe different types of loading.
6)      What is distributed loading? Explain UDL & UVL with examples.
7)      What is a fixed supports? Explain the term reaction moment?
8)      State & explain the principle of superposition.
9)      Show that a force at a point can be reduced to a force-couple system at another point on the same plane.
10)  What is the meaning of Equivalent System?
11)  What is Free Body Diagram or FBD?
12)  Prove that for a belt drive, (T1/T2) = eμθ




 
NUMERICALS: (10 marks)

(1) Two rigid rod BA & CA are joined together at point A as shown in the figure. Now a weight of 200 kN is placed at point A. Find the reaction forces in the rod AB & AC.

    [ RAC = 292.38 kN,  RAB = 155.57 kN]




 
(2) A weight of 40 kN is suspended by two cables as shown in the figure. Find the tensions T1 & T2 in the cables. 








 3) On a square plate ABCD four forces are applied as shown in the figure. Find the resultant of the force system.





         
          4) A uniform bar AB length L and weight W lies in a plane with its ends resting on two smooth surfaces on OA and OB. Find angle θ for equilibrium of bar.

             [θ = 30° ]



Tuesday, 8 November 2011

SHORT QUESTIONS: UNIT-1; FORCE SYSTEM

As new pattern has been issued by MTU for B. Tech first year EME-102 / EME-201:


Section A contains short questions, 2 from each unit & total 10 questions each of 2 marks.
__________________________________________________________________________________

1) What is a Couple?

Ans: Two unlike parallel, non-collinear forces having same magnitude from a Couple. The distance between two forces is known as arm or lever of the couple.

        Properties of a Couple:

        (i) Two unlike parallel, non-collinear forces having same magnitude from a Couple.
       (ii) The resultant of a couple is always zero.
      (iii) The moment of a couple is the product of one of the forces and moment arm of the couple.
      (iv) A couple cannot be balanced by a single force.
       (v) It can be balanced only by another couple of opposite nature.
      (vi) The moment of a couple is independent of the moment center.
     (vii) The effect of a couple is unchanged if
                         (a) it is shifted to any other position in its plane or to any other parallel plane
                         (b) it is rotated through any angle in its plane.



(2) What is Moment of Inertia of a Mass M?


MOI or MOMENTS OF INERTIA is a physical quantity which represents the inertia or resistances shown by the body against the tendency to rotate under the action external forces on the body. It is a rotational axis dependent function as its magnitude depends upon our selection of rotational axis.

If a body of elemental mass dM rotates about an axis r distance from the body, the elemental Mass Moment of Inertia will be r².dM and total moment of inertia of the body of mass M about the axis of rotation will be the integration of the elemental mass moment of inertia ie. ∫r².dM

(3) What is a force system?






a)     State Lami’s theorem of equilibrium of force.
b)    What is Angle of Friction? State coulomb’s Law of Dry Friction.
c)     Explain the Maxwell’s equation of truss.
d)    What is point of contraflexure?
e)     What is area moment of inertia? What is its unit?
f)     What is the difference between centroid and center of gravity?
g)    What is angular acceleration? What is kinetic energy?
h)    What is inertial force?
i)      What is normal stress and normal strain?
j)      Explain the term poisson’s ratio?

Friday, 23 September 2011

TQM, THE CHANGE IN CONCEPT OF QUALITY:

There are several individuals who have made the concept of quality as a full fledged subject having deep theoretical and philosophical base. One of them was W. Edward Deming.

He is one of the best-known "Quality Expert" in the world. Deming was the person who was instrumental in the post-war industrial revival of Japan. As the Japanese industry adopted his methods and witnessed a substantial improvement in quality in products as well as service sectors.

Deming was a strong proponent of the theory that says "Quality is the responsibility of the management." Deming philosophy is summarized in the fourteen points.  



(i) Create Constancy of Purpose for Improvement of Product & Service:

This is nothing but a "Mission Statement" which must be understood by all employees, suppliers and customers.

(ii) "Always ready to adopt the New Philosophy":

Management must understand the connotations of the new philosophy which says, "Quality is a responsibility of the Management". Hence, they must take initiative and the leadership for change wherein poor workmanship, defective products or bad service are not acceptable.

(iii) Cease Dependence on Mass Production


(iv) End the Practice of Awarding Business on the basis of Price Tags alone


(v) Improve consistently and forever the system of production and service


(vi) Institutive training:

Q&A : QUALITY MANAGEMENT AND TQM


 1.      Describe the TQM philosophy and identify its major characteristics.

TQM focuses on identifying the causes of quality problems and correcting these problems.  TQM emphasizes the need to include every employee in the organization in the quality improvement efforts.  TQM emphasizes the need to define quality based on the customer’s needs.  Its major characteristics are customer focus, continuous improvement, and quality at the source, employee empowerment, understanding quality tools, and a team approach, benchmarking and managing supplier quality.



2.      Explain how TQM is different from the traditional notions of quality.  Also, explain the differences between traditional organizations and those that have implemented TQM.

Traditional notions of quality focused on inspection of products.  Instead of relying on inspection as the primary tool for quality, TQM focuses on identifying the causes of quality problems and correcting these problems.  TQM takes a broader view of the organization than traditional views of quality.  Organizations that implemented TQM successfully were able to produce a higher quality product at a lower price, thereby increasing market share. Traditional organizations have either failed or will fail in the future if quality is poor.



3.      Find three local companies that you believe exhibit high quality.  Next find three national or international companies that are recognized for their quality achievements.

The selection of the local companies will depend on the location of the university utilizing this textbook.  The Ritz-Carlton Hotel Company, a winner of the Malcolm Baldrige National Quality Award, is known for outstanding customer service.  Its employees are trained well and are empowered to deal with quality problems on the spot.  Florida Power & Light (FPL) was the first American company to win Japan’s Deming Prize, which is a prestigious quality award.  FPL has created and used a process for identifying and dealing with quality problems that has been benchmarked by a number of companies.  For example, FPL applied this process to the problem of service interruptions to determine the major causes.  They made changes based on the analysis, such as moving power poles away from dangerous curves in the road to deal with one important cause (Florida Power Light Quality Improvement (Q1) Story Exercise (A), Harvard Business School Case 9-689-041).  Disney is well-respected for its customer focus.  Disney has theme parks in the U.S., Japan and Europe.  Disney is known for its excellent training program and attention to details.   



4.      Describe the four dimensions of quality.  Which do you think is most important?

The four dimensions of quality are the quality of product or service design, quality of conformance to design, ease of use and post-sales service.  The quality of product or service design is determined by the features that are included in the final design of the product or service.  The quality of conformance to design is the result of how well the product or service meets its specifications.  Ease of use is determined by the ease of using the product or service, its reliability and its maintainability.  Post-sales service is the level of service provided after the product or service has been purchased. 

The four dimensions of quality are all important in determining quality.  However, quality of design is most important since it determines the ability to meet customer needs, which is the objective.  If the quality of design does not meet customer needs, then it will not matter if the product or service meets it design specifications, is easy to use or is supported by good post-sale service.   



5.      Describe each of the four costs of quality: prevention, appraisal, internal failure, and external failure.  Next, describe how each type of cost would change (increase, decrease or remain the same) if we designed a higher quality product that was easier to manufacture.

Prevention costs are the costs associated with preventing poor quality, such as training, designing a quality product that is easy to manufacture and planning costs.  Appraisal costs are the costs of determining the level of quality and finding defects.  These costs include inspections, product testing and quality audits.  Internal failure costs are the costs associated with finding and dealing with quality problems discovered before the product or service reaches the customer.  Some examples of internal failure costs are rework, scrap and machine downtime due to quality problems.  External failure costs are the costs of poor quality discovered by the customer.  Some examples of external failure costs are product returns, lawsuits and repairs. 

If we designed a higher quality product that was easier to manufacture, then both internal and external failure costs would decrease since we would produce less defective product.  Appraisal costs would probably decrease since we may be able to reduce inspections and quality audits.  Prevention costs would increase since we expended effort to design a better quality product.



6.      Think again about the four costs of quality.  Describe how each would change if we hired more inspectors without changing other aspects of quality.

If we hired more inspectors without changing other aspects of quality, then we would still produce the same number of defects.  However, we would find more, but not necessarily all, of these defects before they reach the customer.  Therefore, internal failure costs will increase, while external failure costs will decrease.  Appraisal costs would increase since we are now paying for more inspectors.  Prevention costs would remain the same since we did not change other aspects of quality.



7.      Explain the meaning of the Plan-do-study-act cycle.  Why is it described as a cycle?

The Plan-do-study-act cycle is a procedure for continuous improvement.  First, a plan is developed after we have documented procedures, collected data and identified problems.  Next, the plan is implemented.  We then study the results of our implementation.  Finally, we act based on the results.  It is described as a cycle since it is an ongoing process or series of steps that is repeated.


8.      Describe the use of quality function deployment (QFD).  Can you find examples in which the voice of the customer was not translated properly into technical requirements?

QFD is a tool for matching customer requirements to technical requirements.  This tool incorporates the customer requirements, the relative importance of the customer requirements, the technical requirements (how we can meet customer requirements), the strength and type of relationships between the customer and technical requirements, the relationships or trade-offs between the different technical requirements and the ratings of the ability of competitors and our company to meet customer requirements into one diagram in order to evaluate all this information in an integrated manner. 

In the airline industry, low prices and direct, non-stop flights are two important customer requirements.  Most airlines have focused on developing a hub-and-spoke system in order to improve efficiencies.  A hub-and-spoke system is one in which many flights stop at a hub city, such as Atlanta, before continuing on to the final destinations, or the spokes.  This limits the ability of the customers to find a direct, non-stop flight to their destination, thus increasing travel time. 

9.      Describe the seven tools of quality control.  Are some more important than others?  Would you use these tools separately or together?  Give some examples of tools that could be used together.

The seven tools of quality control are the cause-an-effect diagram, flowchart, checklist, control chart, scatter diagram, Pareto chart and histogram.  The cause-and-effect diagram, or fishbone diagram, shows all possible causes of one quality problem or defect type (effect), where the causes are separated into categories (or bones) on the diagram.  It is used as a brainstorming tool to determine which causes to investigate.  The flowchart documents the flow of the materials or customer through the steps of the process.  The checklist lists the type of defects, along with a tally of the frequency of each type.  Control charts show plots of samples of a product or service characteristic taken from the process over time.  The control chart helps us determine whether the process is in control, which means that only random variation exists.  Scatter diagrams are plots on an x-y axis used to determine the relationship between two variables.  Pareto charts show the frequency and cumulative percentages of defect types arranged from most frequent to least frequent defect types.  This chart demonstrates which defect types cause the majority of the quality problems or complaints.  A histogram shows the frequency of each quality problem.  

The Pareto chart and cause-and-effect diagram can be effectively used in combination.  First, the Pareto chart is used to identify the problem(s) that cause the highest number of actual defects or complaints.  Next, a common problem becomes the effect on the cause-and-effect diagram.  This diagram then helps us identify causes to investigate in order to solve the problem.       

10.  What is the Malcolm Baldrige National Quality Award?  Why is this award important and what companies have received it in the past?

The Malcolm Baldrige National Quality Award (MBNQA) is an award that was created by U.S. Congress in 1987 to promote quality and improve the trade deficit.  The award is important because it provides an effective framework for improving quality.  Many companies have used the MBNQA framework to improve quality, without an intention of applying for the award.  Some of the companies that have received it are Motorola, AT&T, Xerox, Federal Express and Ritz-Carlton.

11.  What are ISO 9000 standards?  Who were they set by and why?  Can you describe other certifications based on the ISO 9000 certification?

ISO 9000 is a set of standards and a certification program for companies based on a documentation of the quality processes.  The standards were set by the International Organization for Standardization to set a standard for companies doing business.  ISO 14000 is a set of standards that focuses on environmental concerns.  QS 9000 is a set of standards based on ISO 9000 that is geared to the automobile industry.


12.  Who are the three “gurus” of quality control?  Name at least one contribution made by each of them.

The three gurus are Deming, Juran and Crosby.  Deming helped management understand that most quality problems are caused by the processes and systems, not the workers.  Deming motivated the usage of statistical quality control tools for differentiating between common and special causes of variation.  Juran contributed to the quality movement by creating a focus on the definition and costs of quality.  Crosby’s contribution is a result of his argument that quality is free, which is based on that idea that many costs of quality are hard to quantify.



Friday, 16 September 2011

Q&A : QUALITY MANAGEMENT

Q1) Define Quality on the basis of specific Products. Describe the salient features to be incorporated into a product that will raise the User Satisfaction. Or explain the statement, "Quality of a product mainly depends upon User Satisfaction".
click for the answer:

Q2) Describe the change of Concept of Quality. What does TQM mean in the case of Quality? Describe the Evolution of Quality Control into the Total Quality Management.

Q3) What is the significance of Product Development Cycle? Describe the term Product Development Cycle in details.

Q4) Describe the meaning of Quality in Production. What are the stages of Quality in manufacturing?

Q5) What are the salient features of purchasing process? What are the main characteristics of a purchasing process of an organisation that is committed to maintain an excellent quality control?

Q6) What does the term "Quality Assurance" stand for? How does it enhance the quality of a "Product?"

Q7) "ISO-9000 is a "Quality Control Technique".... Explain the sentence.



Tuesday, 13 September 2011

ACTIVITIES OF QUALITY

ACTIVITIES OF QUALITY

In the manufacturing industry, activities concerned with quality can be divided into six stages:

1. Product Planning:
planning for the function, price, life cycle, etc. of the product concerned.

2. Product Design:
designing the product to have the functions decided in product planning.

3. Process Design:
designing the manufacturing process to have the functions decided in the product design.

4. Production:
the process of actually making the product so that it is of the designed quality.

5. Sales:
activities to sell the manufactured product.

6. After-Sales Service:
customer service activities such as maintenance and product services.


It is important to note that company-wide activities are necessary to improve quality and productivity at each of the six stages mentioned above. A company needs to build an overall quality system in which all activities interact to produce products of designed quality with minimum costs.

Note that there are three different characteristics of quality in an overall quality system in the manufacturing industry:

1. Quality of Design:
Quality of product planning, product design and process design.
                              

2. Quality of Conformance:
Quality of production.


3. Quality of Service:
Quality of sales and after-sales services.


Nowadays, these three aspects of quality are equally important in the manufacturing company. If any one of them is not up to the mark, then the overall quality system is unbalanced, and the company will face serious problems.

Although these definitions are somewhat different, some common ideas run through them. Quality involves developing specifications to meet customer needs (quality of design), manufacturing products which satisfy those specifications (quality of conformance), and then providing after-sales services.

However, Taguchi’s definition of product quality is unusual. The loss he refers to may be caused by variability of function, or by harmful side-effects. Hence, if a product costs society no loss, the product is of the best quality, and the poorer the product’s quality is, the greater the cost of the product to the society.

An example of loss caused by variability of function would be an automobile tire that does not last long. The driver would suffer a loss if he replaced the flat tire in the middle of a highway at night because the tire has an unexpectedly short life.

An example of loss caused by a harmful side-effect would be a cold medicine which causes drowsiness in the person who takes it. Then the person would suffer a loss if this drowsiness caused him to be unable to work.

NEXT POST:  Taguchi’s concept of quality engineering from the standpoint of how quality can be designed, manufactured and measured.