Analyzing Students’ Understanding of Work-Energy Concept

Work-energy is one of fundamental concept of physics. There is a subtle distinction among sources, forms and modes of transfer of work-energy process. Moreover, there are different meaning of work-energy in science and daily life which leads to misconception. This paper reported students’ undestanding and the method has been used to teach work-energy concepts. This study was implemented mixed method embedded experimental design. Subject consisted of 57 students of mechanical engineering who took Physics for Engineering course, enrolling in 2018/2019 academic year. Data were analyzed quantitatively are score of student’s conceptual understanding by paired sample t-test. Data were analyzed qualitatively are students’ responses by constant comparative method and interviews. Students’ conceptual understanding score was improved from mean’s score 44,40 to 72,54 (p < 0,01) and effect size was improved with high category (3,79), upper-medium N-gain (0,51). According to students’ respon and interview result, there were students’ difficulties in understanding work-energy such as interpreted work-energy concept in the context of science and used work-energy process. Moreover, teachers found difficulties about the role of language in the teaching of energy.


Introduction
Physics is a subject that explains various natural phenomenon. Natural phenomenon are explained by identifying relevant physics principles [1]. Contextual learning provides problems directly experienced by students, so that after learning students are expected have a good problem solving skills. In addition, from a pedagogical perspective, problem solving can be used to assess learning carried out by students. Physics learning is not only an explanation of principles but also its application to problems. Problem solving is the main element in various disciplines [2]. Students who are trained in problem solving will have a good mindset in creating solutions. The problem solving process trains students to be actively involved in using knowledge innovatively.
Assessing students' problem solving skills requires diagnostic tools (assess the content learned) and evaluation tools (assess their ability to use what is learned [3]. Well-structured physics problem guide unique and unambiguous solutions that are different from solutions to common problems [2]. Therefore, problem solving has an important role in building cognitive abilities during the learning process. Work-Energy concept is one of the important topics in natural science. These topics are also studied from the elementary school level to the university level. It is one of the concepts of science that crosses all disciplines and deals with everyday life situations [4,5]. Jewett [5] states that these concepts are important that are used to analyze physical phenomena. The inequality between everyday understanding and the scientific explanation of the Work-Energy concept leads misconception. In everyday life, the meaning of energy is commonly associated with fuel oil for transportation, electricity for lighting lights and other household appliances, and food to supply the body's needs. Energy is defined as the ability to carry out activities (work). The idea only says that with fuel, electricity and food can do something, they give us something called energy [6] with which we can carry out activities (work). The difference in the meaning of energy between what is meant in science and in everyday life has implications for the vulnerability of misconceptions to students. Research shows that many students experience the wrong concept of energy [7,8]. In addition, several science education studies show that many students and teachers of natural science use erroneous concepts about energy and energy-related concepts [4,9,10].
Work-energy is a difficult concept for students. In general, research shows that there are difficulties in understanding the concept of work-energy among students of all ages [4,11,12]. The concepts of work and energy are quite difficult for college students [13]. In contrary to the concept of force (pull or push), the concept of effort and energy is quite abstract so that the transfer of learning from one context to another is very difficult [13,14].
Students' difficulties in the work-energy concept have not been studied in depth. Several studies have shown that effective instruction in teaching of work-energy concept is quite difficult. Teaching work-energy concept is challenging at all levels of instruction [13,14]. Therefore, it is necessary to analyze students' understanding on the concept of work-energy and design learning that is able to anticipate students' misconception through this research.

Methods
This research was implemented mixed method embedded experimental design [15]. Subject consisted of 57 students of mechanical engineering in University of Nusantara PGRI Kediri, enrolling in 2018/2019 academic year. The data of this study are observational learning, students' conceptual understanding, and interviews. Quantitative data collection was done by test (pretest and posttest). The test instrument consisted of 10 questions. Pretest and posttest used the same instrument, i.e. integrated test developed from Energy and Momentum Conceptual Survey [13] and Mechanics Baseline Test [16]. By integrated test, we designed to assess those learning outcomes simultaneously. In this paper we focus on students' understanding of work-energy concept. Test was used to assess score of students' understanding. After that, it was using SPSS 23 for windows by paired sample t-test. Qualitative data in this research were students' reason and interviews. Students' reason data was obtained from test. In addition to multiple choice, the test also asked students to write down the reason of their answer. After analyzing students' understanding qualitatively, researcher conducted interviews to confirm further information student understanding of work-energy concept. According to students' respon and interview, researcher began to organize and code the data. Based on data code were obtained, it will be interpreted to explain the result. Qualitative data were validated using data triangulation, member checking, and auditing.

Result and Discussion
Quantitative data on students' conceptual understanding were pretest and posttest score. Students' conceptual understanding score was improved from mean's score 44.40 to 72.54 (p < 0,01). The strength of the increase in pretest to posttest was measured using the value of d-effect size and Ngain. From the calculation results, the effect size is 3.79 which indicates that the strength of difference between the posttest and pretest was very large category [17]. While the results of the calculation of N-gain scores were obtained at 0.51 which is included in the upper middle category [18].
Qualitative data were obtained from interview, students' reason from pretest and postest, interview. Students' understanding concept was discussed in this paper are defining work-energy in the context of science and work-energy process. According to pretest and posttest, students' still found difficulties about this concept. Students' understanding basic concept of work-energy is explored through question problem 1 below.

Figure 1.
Question problem 1 that used to analyze students' understanding to define work-energy in scientific meaning adopted from Energy and Momentum Conceptual Survey [13] According to the question above, students' answer during pretest and posttest shown in Table 1. The correct answer is B. Students' difficulties about the relationship between work and gravitational potensial energy can identified through this question. According to Table 1, there are changes in students' answer from the pretest to the posttest. At pretest, there are only 8 students answered correcty (14%). At posttest, there are 34 students answered correctly (60%). This shows that students' understanding is increased. In contrary, there are 23 students (40%) who had misconception. According to the students' responses and interviews, student assumed that if they lift the suitcase quickly and take longer path means that doing more work. In addition, they assosiated with everyday life that doing more work means getting more tired. Therefore, it is important for educators to pay attention to the use of language in teaching. This is in accordance with the results of research which states that one of the difficulties students understand a concept because of the use of ambiguous language [19,20]. Gravitational potential energy is one form of energy. Potential energy is always associated with a system of two or more interacting objects. Serway and Jewett [6] stated that When a small object moves near the surface of the Earth under the influence of gravity, we may sometimes refer to the potential energy "associated with the object" rather than the more proper "associated with the system" because the Earth does not move significantly. To increase the distance of Earth-objects as far as needed external work of mgh. Because the work is positive, the Earth-object system has additional energy. The addition of energy equal to mgh is stored as gravitational potential energy. The amount of work done by the gravitational force depends only on changes in height (h). That is, changes in gravitational potential energy are more important than their own gravitational potential energy. Because only the changes are important, its free to determine the reference point to which gravitational potential energy is given a zero value. In general, the Earth's surface is more often used as a zero point  a suitcase from the floor to a table depends only on  the height of the table above the floor. To prevent students had misconception about work-energy in scientific meaning, we developed a strategy. First, identify students' understanding about work-energy. Through this result, we gave reinforcement that work-energy in everyday life is different from scientific meaning. Second, discuss two form basic energy in scientific (kinetic and potensial energy). At this session, use verbal definition and mathematic equation. After that, engage students to investigate through demonstration or practice, so students have a meaningful understanding. Third, introduce student about work-energy transformation.

Analyzing work-energy process
Students' understanding basic concept of work-energy is explored through question problem 2 below.

Figure 2.
Question problem 2 that used to analyze students' understanding to work-energy peocess adopted from Mechanics Baseline Test [17] According to the question above, students' answer during pretest and posttest shown in Table 2. The correct answer is A. Most of students answer (73,7%) is B that the kinetic energy of object I is greater than that of object II. The reason is the object mass I which is 4 times the mass of object II, so that the kinetic energy of object I is obviously greater than object II. Some of students also used mathematical representation to calculate the kinetic kinergy ( , so that ) In the other hand, students also believed that kinetic energy of object I and object II have a greater kinetic energy at finish line than at the initial position. Students should used the work done by force ( Because the direction of force is same as the diplacement, so the work done by force is (3) If the magnitude of force and diplacement at the initial position are the same, so do the kinetic energy. So, the kinetic energy of this problem is not depends on the mass of the object.
Students' difficulties in this problem because students have not been able to determine the system and environment of a problem. Students' difficulties in determining the system and environment have an impact on students' ignorance of the process of transfer and energy transformation. Students'ignorance of the transfer process and energy transformation is the main reason of students' difficulties in work-energy process [21][22].
To help students forgot a formula-centered problem solving method and acquire a coherent expertlike problem solving strategy, Zhou [23] developed a multiple-representation approach for solving work-energy problems. A work-energy process can be represented in verbal, pictorial, and mathematical representations. The bar chart has represents the conservation of energy. A bar chart usually is an effective external representation to help people reason about information that it represents. The work-energy bar chart can be used as a physical representation for work-energy processes.

Conclusion
We have analyzed a students' conceptual understanding of work-energy concept. We found that students have difficulty in qualitatively interpreting the basic principles related to work-energy concept in applying them in physical situations. This study revealed the students' difficulties such as students were not been able to distinguish energy in the scientific context and everyday life, determine system and environment of work-energy process. These difficulties must be addressed immediately. One of the solution to remediate the students' misconception is emphasize the basic concept and workenergy related concept such as kinematics and Newtons' Law. It was clear from the literature that work-energy was a difficult concept to understand and it was proved in this study. Building concepts through modelling can strengthen understanding of basic concepts of students which are then developed to be applied to other situations.