Question

Work-Energy Theorem:

1. Give an example of an explanation you devised to your friend or classmate to make him/her understand what you were talking about. What representations did you use (analogy, graph, equation etc.) when you were explaining to him/her? Do you think using more than one representation helps you explain better? If so, why do you think it helps?

2. For the same explanation above, please try to identify what assumptions you made. Why did you make the assumption/assumptions? In other words, what do you think are the functions of your assumption(s) when you devise your explanation?

Answer 1

1. The work-energy theorem states that the work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle. We can extend this definition to rigid bodies by defining the work of the torque and rotational kinetic energy.

The work W done by the net force on a particle equals the change in the particle’s kinetic energy :K.E

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Work is the result of force and the resulting displacement. We know, kinetic energy is associated with moving body, there should be relation between work done and kinetic energy.

Consider for example,a test car that is crashed head-on into a heavy, rigid concrete barrier. The directed kinetic energy of the car certainly decreases as the car hits the barrier, crumples up, and comes to rest. However, there are forms of energy other than directed kinetic energy that enters in this situation. There is internal energy associated with the bending and crumpling of the body of the car; some of this internal energy may appear, for instance as an increase in the temperature of the car, and some may be transferred to the surroundings as heat. Note that, even though the barrier may exert a large force on the car during the crash, the force does no work because the point of application of the force on the car does not move.

2. We have assumption that the object behave as the particles, because this law is applicable to oarticles only.