PBL 1 - Student’s Report SF0013 : Mechanics
Tutorial group : 8 Facilitator : JACKSON CHANG MATRIC NO FS16110032 FS16110394 FS16110405 FS16110401 FS16110073 FS16110056
ELEMENT Learning Outcomes Problem Statement General Discussion Specific Questions References
NAME NORAISYAH BINTI MOHD TAHANG MOHAMMAD FADHILAH BIN ASLI MOHAMAD SHAKENDY BIN AHMAD MOHD SYUIB BIN SAINI APHELMINA VICTOR LILYANA CHONG
Mark/s
Note : (1) Please include all the raw results in your full report (2) Full mark for every PBL session is 100%, another 50 marks will be determined from your presentation
LEARNING OUTCOMES After the investigation, students will be able to :
Relate and determine the relationship between the wrecking ball and the buildings
Know the wrecking ball acts by the concept of conservation of energy which is from potential energy into a kinetic energy
Understand the concepts of potential and kinetic energy.
Relate concepts of kinetic and potential energy to real life examples, such as in engineering.
Understand that a wrecking ball has a specific period, regardless of where the weight on wrecking ball is started, or how much it weighs.
Use the concepts of conservation of energy in daily life
Use the concepts of conservation of energy to perfome some projects to determine the object’s velocity.
PROBLEM STATEMENT One of the oldest and most commonly used methods for building demolition, the ball and crane use a wrecking ball weighing up to 13,500 pounds to demolish concrete and masonry structures. During the process, the ball is either dropped onto or swung into the structure that is to be demolished. The ball and crane, however, is unsuitable for all demolition applications. We have planned to demolish a building. It gives a task to prevent the neighbourhood environment from damage, repair of damage structures, construction of other structure at that previously constructed site and provide safety for the occupants in the building. A method statement showing how the demolition work is to be carried out and should be prepared and we will appoint a "competent person" to supervise the demolition work. As an intrinsic part of the construction process, efficient demolition of structures is an important factors deserving careful consideration in the evolution of any redevelopment project. Modern emphasis is on reduction of construction periods to ensure economic redevelopment, coupled with increasing town centre regenerating calling for careful demolition on constructed and restricted site, have resulted in more consideration being given to demolition as part of the process of construction and redevelopment than was typical in previous times. The strategy will need to take into account the method of construction used for the original building and its proximity to other buildings, structures and the general public. These factors, together with location, the cost and availability of tipping and disposal and the desirability and economics of reuse, must be taken into account in the development of an appropriate strategy for the demolition of a structure. Information on buildings in terms of "as built" drawings and structural details may often be unavailable or unreliable, and consequently some investigative site and desk work may be necessary, both to ascertain the way in which the building was originally constructed, and to identify the stresses and strains which exist between it. In order to plan the most efficient method of demolition, it is important to have a full understanding of the method of construction and the stress patterns imposed upon the building. Failure to do so may result in risks to the safety of both those involved in the demolition and those in close proximity to the site.
GENERAL DISCUSSION
DIAGRAM 1 Based on the video clip, the situation that was shown was the wrecked of a wrecking ball to an abandoned house. As the wrecking ball wrecked the house, the house collapse as the structure of the house started to separate to each other. Basically, the wrecking ball situation was same as the situation of the swinging pendulum bob. Diagram 1 showed how the wrecking ball situation is happened which is the same as the swinging pendulum bob. The first physic concept that is involved is CONSERVATION OF ENERGY. The law of conservation of energy states that the total energy of a closed system remains constant. Energy in the closed system can neither be created nor destroyed, and can only change form. In this case, the wrecking ball is moved from its rest point (A) to swing to the maximum points (B&C). At the point A, the kinetic energy is at maximum. As the formula is 1/2mv^2, the velocity of the wrecking ball is being doubled made the KE becomes the maximum. While at point C and B, the potential energy is at maximum value. The formula for PE is mgh. As at point C and B are at the highest height, the potential energy is at maximum value. The total energy at A, B and C are the same due to conservation of energy. The swinging of wrecking ball is actually involved the changing state of energy which are between kinetic energy and potential energy. The energy that involve at point between A&B and A&C are PE AND KE.
DIAGRAM 2 Furthermore, the second physic concept is momentum. As the wrecking ball hits the house momentum is occur. The formula is momentum = mv. The wrecking ball is a moving object thus it has the velocity. The momentum value depends on the value of mass and velocity of object. When the mass and velocity increase, the momentum also increases. The law conservation of momentum occurs as the total momentum before collision and after collision are the same. In this situation, the collision involve is inelastic collision. This is because, the direction of the wrecking ball and wall of the house are the same. Then, the third physic concept is the impulsive force. The change of momentum occur in the wrecking ball thus, the impulse occur. As in the video clip the wrecking ball hits the wall of the house until it collapse. At some time, the impulsive force happened. The formula of impulsive force is
(mv-
mu)/t. the value of impulsive force increases as the time impact decreases. If the wrecking ball needs to wreck with higher impulsive force, a shorter time should be made. Therefore, there are three main physic concepts that we find through the video clip. They are conservation of energy, conservation of momentum and the impulsive force.
SPECIFIC QUESTIONS 1.
2. Varying the mass of the wrecking ball does not increase the frequency of oscillation. The mass of the wrecking ball does not affect the frequency of oscillation because the acceleration is constant. Only the length of chain or string and the starting angle of pendulum affect the frequency of oscillations. 3. When it is at the highest point, the potential energy is at maximum, but there is no kinetic energy. As the wrecking ball oscillates, at the lowest the kinetic energy is at the maximum but the potential energy becomes zero. It shows that the potential energy is converted to kinetic. This prove that the movement of wrecking ball does apply the principle of conservation of energy. The conservation of momentum is shown when the wrecking ball collides with the building , thus, converting the momentum from the ball to the building. In physics mechanical energy is the sum of kinetic and potential energy in an object that is used to do work. In other words, it is energy in an object due to its motion or position, or both. Mechanical energy is often defined as the ability to do work. So, in this case, the potential energy and kinetic energy are the reasons why the wrecking ball is able to do work. The wrecking ball is a massive object that is swung backwards to a high position and allowed to swing forward into building structure or other object in order to demolish it. Upon hitting the structure, the wrecking ball applies a force to it in order to cause the wall of the structure to be destructed.
4. Height that should be used to raise the wrecking ball, h
∑ E at lowest point = ∑ E at highest point
+ -Maximum height that the wrecking ball could be raised, H
REFERENCES
~Lin Poh Tin. (2015). Work, Energy and Power. In P. L. yong, STPM Physics (p. 50). Selangor: Pelangi Sdn.Bhd. ~(2015). Momentum and Impulse. In L. K. Poh Liong Yong, for matriculation PHYSICS (Term 1) (p. 33). Selangor Darul Ehsan: Oxford Fajar Sdn.Bhd. ~Yap Eng Keat, T. I. (2013). Forces and Motion. In eNotes SPM (pp. 26-43). Kuala lumpur: Pearson Malaysia Sdn.Bhd.
