Energy principle example problem in classical mechanics book

In summary, a man with a mass of 100 kg can pull a rope with a maximum force of 200 N, which is two fifths of his own weight. In a competition, he must pull a block of mass 1600 kg across a smooth horizontal floor, and is able to apply his maximum force for 12 seconds before becoming exhausted. The total work done by the man is 2400 J, and this example confirms the work-energy principle. However, there may be a typo in the textbook as the problem states the man's maximum force is 2/5 of his weight, which would be 400 N, not 200 N.
  • #1
certainice
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Homework Statement


A man of mass 100 kg can pull on a rope with a maximum force equal to two fifths of his own weight. [Take g = 10 ms^2] In a competition, he must pull a block of mass 1600 kg across a smooth horizontal floor, the block being initially at rest. He is able to apply his maximum force horizontally for 12 seconds before falling exhausted. Find the total work done by the man and confirm that the energy principle is true in this case.

Homework Equations


F*v*dt=W , Work-Energy principle

The Attempt at a Solution



0http://physics.stackexchange.com/questions/279513/energy-principle-example-problem-in-mechanics-book# The problem as stated in the book Classical Mechanics by R Douglas Gregoryhttps://books.google.co.uk/books?id...equal to two fifths of his own weight"&f=false .I only have an issue with a portion of the problem.Part of the solution to that example problem states that the force he applies is a constant 200 N. But shouldn't it be 400 N since the problem states that he pulls with a maximum force of two-fifths of his own weight and his weight is 1000 N and two-fifths *1000 is 400 N? Maybe I am missing something here.
 
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  • #2
Hi certainice, Welcome to Physics Forums!

It's not unheard of for there to be typos in textbooks, particularly if example problems are "updated" for new editions. 2/5 of 1000 is indeed 400, not 200.

Do the derivation yourself symbolically rather than plugging in numbers, or just show that your own numerical results demonstrate the principle being examined.
 

1. What is the Energy Principle in Classical Mechanics?

The Energy Principle, also known as the Conservation of Energy, is a fundamental principle in classical mechanics that states that energy cannot be created or destroyed, but only transferred or transformed from one form to another.

2. How is the Energy Principle used in solving problems in classical mechanics?

The Energy Principle is used to analyze the motion of objects by considering the different forms of energy involved, such as kinetic energy, potential energy, and work. It allows for the prediction of an object's motion without having to consider the specific forces acting on it.

3. What is an example problem that demonstrates the use of the Energy Principle in classical mechanics?

One example problem could be a simple pendulum, where the potential energy of the pendulum bob at its highest point is equal to the kinetic energy at its lowest point. By using the Energy Principle, we can determine the speed of the pendulum at any point in its motion.

4. Can the Energy Principle be applied to all systems in classical mechanics?

Yes, the Energy Principle is a fundamental principle in classical mechanics and can be applied to all systems, including simple systems like a pendulum and complex systems like a multi-body system.

5. What are the limitations of the Energy Principle in classical mechanics?

The Energy Principle assumes that there is no external work done on a system, which may not always be the case in real-world situations. It also does not account for potential energy losses due to friction or other dissipative forces, which may affect the accuracy of the predictions made using this principle.

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