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Homework Help: Energy transformations

  1. May 30, 2008 #1
    1. The problem statement, all variables and given/known data

    It is often stated that many forms of transport transform chemical energy into kinetic energy. Explain why a cyclist traveling at constant speed is not making this transformation. Explain what transformations of energy are taking place.

    3. The attempt at a solution

    1. constant speed => no acceleration => no resultant force => no work done
    2. constant speed => no change in kinetic energy.

    i came up with two answers for the first part. i don't know which one of them i should choose.

    for the second part, i think that the transformation involved is that of something being transformed into heat due to friction. but i don't know what is this 'something'.
  2. jcsd
  3. May 30, 2008 #2
    The thing here is that you are contradicting yourself. Firstly, you say that constant speed = no acceleration. However, the work done is defined as Force x displacement. Although you are right that there is no net force, there is a constant force exerted by the cyclist so as to counteract frictional forces. If you consider no work to be done due to constant velocity, you need to consider that there is no friction. But in your answer for the 2nd question, you again assume friction to act.

    I think the question is wrong.. because we are converting the food we eat into mechanical energy with which we can, say, ride a cycle. The food has 'chemical energy', which is converted into chemical energy. And hence, if the cyclist is working against friction, then the conversion of energy is from chemical to kinetic energy. however, there are many other forms it is converted to... [for ex. heat radiation.. as body temperature rises], but that need not be considered for now.
  4. May 30, 2008 #3
    that's what i initially thought. there has to be work done by the cyclist. but i needed an answer... :) at least i would get some marks somewhere.

    there is no gain in Ek since there is no increase in speed. Maybe i should consider the direct conversion of chemical energy into heat and sound energy because of friction and air resistance.
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